diff --git a/lib/ResponseDefinitions.php b/lib/ResponseDefinitions.php
index 096b026be3..6d46e07610 100644
--- a/lib/ResponseDefinitions.php
+++ b/lib/ResponseDefinitions.php
@@ -142,7 +142,7 @@
  * @psalm-type LibresignSignerSummary = array{
  *     signRequestId: int,
  *     displayName: string,
- *     email: string,
+ *     email?: ?string,
  *     identifyMethods?: LibresignIdentifyMethod[],
  *     signed: ?string,
  *     status: int,
@@ -394,7 +394,7 @@
  *     statusText: string,
  *     nodeId: non-negative-int,
  *     nodeType: 'file'|'envelope',
- *     signatureFlow: int,
+ *     signatureFlow: 0|1|2,
  *     docmdpLevel: int,
  *     filesCount: int<0, max>,
  *     files: list<LibresignValidatedChildFile>,
diff --git a/openapi-full.json b/openapi-full.json
index 9ab790941c..d56503b4fb 100644
--- a/openapi-full.json
+++ b/openapi-full.json
@@ -2437,7 +2437,6 @@
                 "required": [
                     "signRequestId",
                     "displayName",
-                    "email",
                     "signed",
                     "status",
                     "statusText"
@@ -2451,7 +2450,8 @@
                         "type": "string"
                     },
                     "email": {
-                        "type": "string"
+                        "type": "string",
+                        "nullable": true
                     },
                     "identifyMethods": {
                         "type": "array",
@@ -2768,7 +2768,12 @@
                     },
                     "signatureFlow": {
                         "type": "integer",
-                        "format": "int64"
+                        "format": "int64",
+                        "enum": [
+                            0,
+                            1,
+                            2
+                        ]
                     },
                     "docmdpLevel": {
                         "type": "integer",
diff --git a/openapi.json b/openapi.json
index 0205a793e2..0c8286187b 100644
--- a/openapi.json
+++ b/openapi.json
@@ -1839,7 +1839,6 @@
                 "required": [
                     "signRequestId",
                     "displayName",
-                    "email",
                     "signed",
                     "status",
                     "statusText"
@@ -1853,7 +1852,8 @@
                         "type": "string"
                     },
                     "email": {
-                        "type": "string"
+                        "type": "string",
+                        "nullable": true
                     },
                     "identifyMethods": {
                         "type": "array",
@@ -2156,7 +2156,12 @@
                     },
                     "signatureFlow": {
                         "type": "integer",
-                        "format": "int64"
+                        "format": "int64",
+                        "enum": [
+                            0,
+                            1,
+                            2
+                        ]
                     },
                     "docmdpLevel": {
                         "type": "integer",
diff --git a/playwright/e2e/sign-email-token-unauthenticated.spec.ts b/playwright/e2e/sign-email-token-unauthenticated.spec.ts
index c618412eef..237e7ab8c3 100644
--- a/playwright/e2e/sign-email-token-unauthenticated.spec.ts
+++ b/playwright/e2e/sign-email-token-unauthenticated.spec.ts
@@ -64,6 +64,30 @@ test('sign document with email token as unauthenticated signer', async ({ page }
 	const email = await waitForEmailTo(mailpit, 'signer01@libresign.coop', 'LibreSign: There is a file for you to sign')
 	const signLink = extractSignLink(email.Text)
 	if (!signLink) throw new Error('Sign link not found in email')
+
+	// Regression guard: validation payload can contain signer without email.
+	// Reuse this existing E2E flow and force `email = null` in the validate response.
+	await page.route('**/ocs/v2.php/apps/libresign/api/v1/file/validate/uuid/**', async (route) => {
+		const response = await route.fetch()
+		const payload = await response.json() as Record<string, unknown>
+		const ocs = payload.ocs as Record<string, unknown> | undefined
+		const data = ocs?.data as Record<string, unknown> | undefined
+
+		if (data && Array.isArray(data.signers) && data.signers.length > 0) {
+			const firstSigner = data.signers[0] as Record<string, unknown>
+			firstSigner.email = null
+		}
+
+		await route.fulfill({
+			status: response.status(),
+			headers: {
+				...response.headers(),
+				'content-type': 'application/json',
+			},
+			body: JSON.stringify(payload),
+		})
+	})
+
 	await page.goto(signLink);
 	await page.getByRole('button', { name: 'Sign the document.' }).click();
 	await page.getByRole('textbox', { name: 'Email' }).click();
@@ -84,6 +108,7 @@ test('sign document with email token as unauthenticated signer', async ({ page }
 	await page.getByRole('button', { name: 'Sign document' }).click();
 	await page.waitForURL('**/validation/**');
 	await expect(page.getByText('This document is valid')).toBeVisible();
+	await expect(page.getByText('Failed to validate document')).not.toBeVisible();
 	await expect(page.getByText('Congratulations you have')).toBeVisible();
 	await expect(page.getByRole('button', { name: 'Sign the document.' })).not.toBeVisible();
 });
diff --git a/src/components/Request/SignDetail/partials/SignerRow.vue b/src/components/Request/SignDetail/partials/SignerRow.vue
index 391cff8478..b3d9bf4aa7 100644
--- a/src/components/Request/SignDetail/partials/SignerRow.vue
+++ b/src/components/Request/SignDetail/partials/SignerRow.vue
@@ -11,7 +11,7 @@
 		<template #icon>
 			<NcAvatar is-no-user
 				:size="44"
-				:user="signer.email"
+				:user="signer.email ?? undefined"
 				:display-name="displayName" />
 		</template>
 		<template #subname>
diff --git a/src/components/validation/SignerDetails.vue b/src/components/validation/SignerDetails.vue
index 0088c45e03..89e2ef89c2 100644
--- a/src/components/validation/SignerDetails.vue
+++ b/src/components/validation/SignerDetails.vue
@@ -284,7 +284,7 @@ type SignerModifications = {
 
 type SignerModel = {
 	displayName?: string
-	email?: string
+	email?: string | null
 	name?: string
 	remote_address?: string
 	user_agent?: string
diff --git a/src/services/validationDocument.ts b/src/services/validationDocument.ts
index 4cfcb816cb..62a22d30d3 100644
--- a/src/services/validationDocument.ts
+++ b/src/services/validationDocument.ts
@@ -32,6 +32,8 @@ export type ValidationModificationInfo = {
 	valid?: boolean
 }
 
+type ValidationSignatureFlow = ValidationFileRecord['signatureFlow']
+
 type ValidationMetadataDimension = {
 	w: number
 	h: number
@@ -64,15 +66,12 @@ function isOptionalField(record: UnknownRecord, key: string, guard: (value: unkn
 }
 
 function toNumber(value: unknown): number | null {
-	if (typeof value === 'number' && Number.isFinite(value)) {
-		return value
-	}
-
-	if (typeof value === 'string' && /^-?\d+$/.test(value)) {
-		return Number.parseInt(value, 10)
-	}
+	return typeof value === 'number' && Number.isFinite(value) ? value : null
+}
 
-	return null
+function toInteger(value: unknown): number | null {
+	const normalized = toNumber(value)
+	return normalized !== null && Number.isInteger(normalized) ? normalized : null
 }
 
 function isString(value: unknown): value is string {
@@ -84,7 +83,7 @@ function isNullableString(value: unknown): value is string | null {
 }
 
 function isValidationStatus(value: unknown): value is ValidationStatus {
-	const normalizedValue = toNumber(value)
+	const normalizedValue = toInteger(value)
 	return normalizedValue === FILE_STATUS.DRAFT
 		|| normalizedValue === FILE_STATUS.ABLE_TO_SIGN
 		|| normalizedValue === FILE_STATUS.PARTIAL_SIGNED
@@ -93,19 +92,22 @@ function isValidationStatus(value: unknown): value is ValidationStatus {
 }
 
 function isSignerStatus(value: unknown): value is SignerDetailRecord['status'] {
-	const normalizedValue = toNumber(value)
+	const normalizedValue = toInteger(value)
 	return normalizedValue === SIGN_REQUEST_STATUS.DRAFT
 		|| normalizedValue === SIGN_REQUEST_STATUS.ABLE_TO_SIGN
 		|| normalizedValue === SIGN_REQUEST_STATUS.SIGNED
 }
 
-function isValidationSignatureFlow(value: unknown): boolean {
-	if (value === 'none' || value === 'parallel' || value === 'ordered_numeric') {
-		return true
+function isValidationSignatureFlow(value: unknown): value is ValidationSignatureFlow {
+	return value === 0 || value === 1 || value === 2
+}
+
+function normalizeValidationSignatureFlow(value: unknown): ValidationSignatureFlow | null {
+	if (isValidationSignatureFlow(value)) {
+		return value
 	}
 
-	const normalizedValue = toNumber(value)
-	return normalizedValue === 0 || normalizedValue === 1 || normalizedValue === 2
+	return null
 }
 
 function isValidationStatusInfo(value: unknown): value is ValidationStatusInfo {
@@ -113,7 +115,7 @@ function isValidationStatusInfo(value: unknown): value is ValidationStatusInfo {
 		return false
 	}
 
-	return isOptionalField(value, 'id', fieldValue => typeof fieldValue === 'number')
+	return isOptionalField(value, 'id', fieldValue => toInteger(fieldValue) !== null)
 		&& isOptionalField(value, 'label', isString)
 }
 
@@ -153,7 +155,7 @@ function isValidationMetadata(value: unknown): value is NonNullable<ValidationFi
 		return false
 	}
 
-	if (!isString(value.extension) || typeof value.p !== 'number') {
+	if (!isString(value.extension) || toInteger(value.p) === null) {
 		return false
 	}
 
@@ -181,9 +183,9 @@ function isSignerDetailRecord(value: unknown): value is SignerDetailRecord {
 		return false
 	}
 
-	return typeof value.signRequestId === 'number'
+	return toInteger(value.signRequestId) !== null
 		&& isString(value.displayName)
-		&& isString(value.email)
+		&& isOptionalField(value, 'email', isNullableString)
 		&& isNullableString(value.signed)
 		&& isSignerStatus(value.status)
 		&& isString(value.statusText)
@@ -203,13 +205,13 @@ function isValidatedChildFileRecord(value: unknown): value is ValidatedChildFile
 		return false
 	}
 
-	return typeof value.id === 'number'
+	return toInteger(value.id) !== null
 		&& isString(value.uuid)
 		&& isString(value.name)
 		&& isValidationStatus(value.status)
 		&& isString(value.statusText)
-		&& typeof value.nodeId === 'number'
-		&& typeof value.size === 'number'
+		&& toInteger(value.nodeId) !== null
+		&& toInteger(value.size) !== null
 		&& Array.isArray(value.signers)
 		&& isString(value.file)
 		&& isValidationMetadata(value.metadata)
@@ -220,19 +222,19 @@ function isValidationDocumentRecord(data: unknown): data is ValidationFileRecord
 		return false
 	}
 	if (
-		typeof data.id !== 'number'
+		toInteger(data.id) === null
 		|| !isString(data.uuid)
 		|| !isString(data.name)
 		|| !isValidationStatus(data.status)
 		|| !isString(data.statusText)
-		|| typeof data.nodeId !== 'number'
+		|| toInteger(data.nodeId) === null
 		|| (data.nodeType !== 'file' && data.nodeType !== 'envelope')
-		|| !isValidationSignatureFlow(data.signatureFlow)
-		|| toNumber(data.docmdpLevel) === null
-		|| toNumber(data.filesCount) === null
+		|| normalizeValidationSignatureFlow(data.signatureFlow) === null
+		|| toInteger(data.docmdpLevel) === null
+		|| toInteger(data.filesCount) === null
 		|| !Array.isArray(data.files)
-		|| toNumber(data.totalPages) === null
-		|| toNumber(data.size) === null
+		|| toInteger(data.totalPages) === null
+		|| toInteger(data.size) === null
 		|| !isString(data.pdfVersion)
 		|| !isString(data.created_at)
 		|| !isRequestedBy(data.requested_by)
@@ -278,24 +280,113 @@ export function toValidationDocument(data: unknown): ValidationDocumentState | n
 		return null
 	}
 
+	const id = toInteger(data.id)
+	const nodeId = toInteger(data.nodeId)
+	const docmdpLevel = toInteger(data.docmdpLevel)
+	const filesCount = toInteger(data.filesCount)
+	const totalPages = toInteger(data.totalPages)
+	const size = toInteger(data.size)
+	const signatureFlow = normalizeValidationSignatureFlow(data.signatureFlow)
+
+	if (
+		id === null
+		|| nodeId === null
+		|| docmdpLevel === null
+		|| filesCount === null
+		|| totalPages === null
+		|| size === null
+		|| signatureFlow === null
+	) {
+		return null
+	}
+
+	const files = data.files.map((file) => {
+		const childId = toInteger(file.id)
+		const childNodeId = toInteger(file.nodeId)
+		const childSize = toInteger(file.size)
+		const childStatus = toInteger(file.status)
+		const metadataPages = toInteger(file.metadata.p)
+
+		if (
+			childId === null
+			|| childNodeId === null
+			|| childSize === null
+			|| childStatus === null
+			|| metadataPages === null
+		) {
+			return null
+		}
+
+		return {
+			...file,
+			id: childId,
+			nodeId: childNodeId,
+			size: childSize,
+			status: childStatus,
+			metadata: {
+				...file.metadata,
+				p: metadataPages,
+			},
+		}
+	})
+
+	if (files.some(file => file === null)) {
+		return null
+	}
+	const normalizedFiles = files.filter((file): file is ValidatedChildFileRecord => file !== null)
+
 	const metadata = isValidationMetadata(data.metadata)
 		? data.metadata
 		: {
 			...DEFAULT_VALIDATION_METADATA,
-			p: data.totalPages,
+			p: totalPages,
 		}
 
+	const metadataPages = toInteger(metadata.p)
+	if (metadataPages === null) {
+		return null
+	}
+
 	const settings = isValidationSettings(data.settings)
 		? data.settings
 		: DEFAULT_VALIDATION_SETTINGS
 
-	const signers = Array.isArray(data.signers) ? data.signers : []
+	const signers = (Array.isArray(data.signers) ? data.signers : []).map((signer) => {
+		const signRequestId = toInteger(signer.signRequestId)
+		const status = toInteger(signer.status)
+
+		if (signRequestId === null || status === null) {
+			return null
+		}
+
+		return {
+			...signer,
+			signRequestId,
+			status,
+		}
+	})
+
+	if (signers.some(signer => signer === null)) {
+		return null
+	}
+	const normalizedSigners = signers.filter((signer): signer is SignerDetailRecord => signer !== null)
 
 	return {
 		...data,
-		metadata,
+		id,
+		nodeId,
+		signatureFlow,
+		docmdpLevel,
+		filesCount,
+		totalPages,
+		size,
+		files: normalizedFiles,
+		metadata: {
+			...metadata,
+			p: metadataPages,
+		},
 		settings,
-		signers,
+		signers: normalizedSigners,
 	}
 }
 
diff --git a/src/services/visibleElementsService.ts b/src/services/visibleElementsService.ts
index bffd835603..6524c74227 100644
--- a/src/services/visibleElementsService.ts
+++ b/src/services/visibleElementsService.ts
@@ -13,7 +13,7 @@ import type {
 export type SignerLike = {
 	signRequestId?: number
 	displayName?: string
-	email?: string
+	email?: string | null
 	identifyMethods?: IdentifyMethodRecord[]
 	signed?: string | null | boolean | unknown[]
 	status?: number
diff --git a/src/tests/services/validationDocument.spec.ts b/src/tests/services/validationDocument.spec.ts
index 832a01b877..1712b2c5e0 100644
--- a/src/tests/services/validationDocument.spec.ts
+++ b/src/tests/services/validationDocument.spec.ts
@@ -106,18 +106,33 @@ describe('validationDocument', () => {
 		}))
 	})
 
-	it('accepts validation payload when signatureFlow is enum string and numeric fields are numeric strings', () => {
+	it('rejects payload with string values in numeric contract fields', () => {
 		const normalized = toValidationDocument(createValidationPayload({
-			signatureFlow: 'none',
-			docmdpLevel: '2',
+			id: '100',
+			nodeId: '100',
+			signatureFlow: 'parallel',
+			docmdpLevel: '0',
 			filesCount: '1',
 			totalPages: '1',
 			size: '10',
-			signers: [createSigner({ status: '2' })],
+			signers: [createSigner({ signRequestId: '1', status: '1' })],
+			files: [{
+				id: '100',
+				uuid: '550e8400-e29b-41d4-a716-446655440000',
+				name: 'contract.pdf',
+				status: '1',
+				statusText: 'Pending',
+				nodeId: '100',
+				totalPages: 1,
+				size: '10',
+				pdfVersion: '1.7',
+				signers: [],
+				file: '/apps/libresign/p/pdf/550e8400-e29b-41d4-a716-446655440000',
+				metadata: { extension: 'pdf', p: '1' },
+			}],
 		}))
 
-		expect(normalized).not.toBeNull()
-		expect(normalized?.signatureFlow).toBe('none')
+		expect(normalized).toBeNull()
 	})
 
 	it('rejects payload with invalid signer status', () => {
@@ -128,6 +143,67 @@ describe('validationDocument', () => {
 		expect(normalized).toBeNull()
 	})
 
+	it('accepts production-shaped payload when signer email is null', () => {
+		const normalized = toValidationDocument(createValidationPayload({
+			uuid: '72a2d63b-772b-4ed7-8b79-5d5b1549fd15',
+			id: 551,
+			nodeId: 28111,
+			signatureFlow: 0,
+			docmdpLevel: 2,
+			filesCount: 1,
+			totalPages: 1,
+			size: 182873,
+			status: FILE_STATUS.SIGNED,
+			statusText: 'Signed',
+			created_at: '2026-04-23T20:46:58+00:00',
+			requested_by: { userId: 'owner', displayName: null },
+			signers: [createSigner({
+				signRequestId: 637,
+				displayName: 'External signer',
+				email: null,
+				status: SIGN_REQUEST_STATUS.SIGNED,
+				statusText: 'Signed',
+				request_sign_date: '2026-04-23T20:46:58+00:00',
+				me: false,
+			})],
+			files: [{
+				id: 551,
+				uuid: '72a2d63b-772b-4ed7-8b79-5d5b1549fd15',
+				name: 'document.pdf',
+				status: FILE_STATUS.SIGNED,
+				statusText: 'Signed',
+				nodeId: 28111,
+				totalPages: 1,
+				size: 182873,
+				pdfVersion: '1.7',
+				signers: [],
+				file: '/apps/libresign/p/pdf/72a2d63b-772b-4ed7-8b79-5d5b1549fd15',
+				metadata: {
+					extension: 'pdf',
+					p: 1,
+					d: [{ w: 595.3, h: 841.9 }],
+					pdfVersion: '1.7',
+					status_changed_at: '2026-04-23T20:57:29+00:00',
+				},
+			}],
+		}))
+
+		expect(normalized).not.toBeNull()
+		expect(normalized?.signers[0]?.email).toBeNull()
+	})
+
+	it('accepts payload when signer email is omitted', () => {
+		const signerWithoutEmail = createSigner()
+		delete signerWithoutEmail.email
+
+		const normalized = toValidationDocument(createValidationPayload({
+			signers: [signerWithoutEmail],
+		}))
+
+		expect(normalized).not.toBeNull()
+		expect(Object.prototype.hasOwnProperty.call(normalized?.signers[0] ?? {}, 'email')).toBe(false)
+	})
+
 	it.each([
 		['status null', { status: null }],
 		['status outside allowed values', { status: 99 }],
diff --git a/src/types/openapi/openapi-full.ts b/src/types/openapi/openapi-full.ts
index cb21c1a4b1..2bc6b201c6 100644
--- a/src/types/openapi/openapi-full.ts
+++ b/src/types/openapi/openapi-full.ts
@@ -2210,7 +2210,7 @@ export type components = {
             /** Format: int64 */
             signRequestId: number;
             displayName: string;
-            email: string;
+            email?: string | null;
             identifyMethods?: components["schemas"]["IdentifyMethod"][];
             signed: string | null;
             /** Format: int64 */
@@ -2302,8 +2302,11 @@ export type components = {
             nodeId: number;
             /** @enum {string} */
             nodeType: "file" | "envelope";
-            /** Format: int64 */
-            signatureFlow: number;
+            /**
+             * Format: int64
+             * @enum {integer}
+             */
+            signatureFlow: 0 | 1 | 2;
             /** Format: int64 */
             docmdpLevel: number;
             /** Format: int64 */
diff --git a/src/types/openapi/openapi.ts b/src/types/openapi/openapi.ts
index 05c59f901e..92dd34df6b 100644
--- a/src/types/openapi/openapi.ts
+++ b/src/types/openapi/openapi.ts
@@ -1565,7 +1565,7 @@ export type components = {
             /** Format: int64 */
             signRequestId: number;
             displayName: string;
-            email: string;
+            email?: string | null;
             identifyMethods?: components["schemas"]["IdentifyMethod"][];
             signed: string | null;
             /** Format: int64 */
@@ -1653,8 +1653,11 @@ export type components = {
             nodeId: number;
             /** @enum {string} */
             nodeType: "file" | "envelope";
-            /** Format: int64 */
-            signatureFlow: number;
+            /**
+             * Format: int64
+             * @enum {integer}
+             */
+            signatureFlow: 0 | 1 | 2;
             /** Format: int64 */
             docmdpLevel: number;
             /** Format: int64 */