diff --git a/.changeset/24750-invite-role-not-found-code.md b/.changeset/24750-invite-role-not-found-code.md
new file mode 100644
index 00000000000..8b8d81b4285
--- /dev/null
+++ b/.changeset/24750-invite-role-not-found-code.md
@@ -0,0 +1,13 @@
+---
+'@objectstack/plugin-auth': minor
+'@objectstack/spec': minor
+---
+
+fix(plugin-auth): `POST /api/v1/auth/organization/invite-member` refuses a role outside the membership vocabulary with `code: 'ROLE_NOT_FOUND'`
+
+Clause-②: yes (widening)
+
+- **Before.** An invitation naming a role outside the closed membership vocabulary was refused `400` with only a message (`ROLE_NOT_FOUND: <role>`) and no `code`, so a client that branches on `error.code` (ADR-0112) could not recognise it. `update-member-role` already answered the same refusal with `code: 'ROLE_NOT_FOUND'`.
+- **Now.** invite-member answers `400` with `code: 'ROLE_NOT_FOUND'` and the same message, naming the role, the body `update-member-role` gives for the same condition. The refusal still happens before any invitation row is written. This is the answer the invitation schema's `role` docstring and the authentication docs already promise.
+- **The ledger.** `ROLE_NOT_FOUND` is registered under `@objectstack/plugin-auth` in the error-code ledger, so `ErrorCode` (and `ApiErrorSchema.code`) admits it.
+- **Unchanged.** A valid role invites as before, and every other refusal on invite-member keeps its answer.
diff --git a/content/docs/references/api/contract.mdx b/content/docs/references/api/contract.mdx
index b9d95113cd7..d542c87a612 100644
--- a/content/docs/references/api/contract.mdx
+++ b/content/docs/references/api/contract.mdx
@@ -28,7 +28,7 @@ const result = ApiErrorSchema.parse(data);
 
 | Property | Type | Required | Description |
 | :--- | :--- | :--- | :--- |
-| **code** | `Enum<'VALIDATION_ERROR' \| 'INVALID_FIELD' \| 'MISSING_REQUIRED_FIELD' \| 'INVALID_FORMAT' \| 'VALUE_TOO_LONG' \| 'VALUE_TOO_SHORT' \| 'VALUE_OUT_OF_RANGE' \| … +339 more>` | ✅ | Error code (e.g. VALIDATION_ERROR; StandardErrorCode ∪ the ledger the serving side registers — ERROR_CODE_LEDGER for framework packages) |
+| **code** | `Enum<'VALIDATION_ERROR' \| 'INVALID_FIELD' \| 'MISSING_REQUIRED_FIELD' \| 'INVALID_FORMAT' \| 'VALUE_TOO_LONG' \| 'VALUE_TOO_SHORT' \| 'VALUE_OUT_OF_RANGE' \| … +340 more>` | ✅ | Error code (e.g. VALIDATION_ERROR; StandardErrorCode ∪ the ledger the serving side registers — ERROR_CODE_LEDGER for framework packages) |
 | **declaredCode** | `string` | optional | The producer-declared code, verbatim, when it is not a member of the closed `code` vocabulary — the open, author-authored channel (app-specific spellings; ADR-0112) |
 | **message** | `string` | ✅ | Readable error message |
 | **userMessage** | `string` | optional | Producer-marked user-facing refusal text, verbatim. Present exactly when the producer opted in at throw time; consumers render it to end users and keep their generic substitution for anything unmarked. Status-agnostic; never replaces `message`. |
@@ -311,6 +311,7 @@ const result = ApiErrorSchema.parse(data);
 * `RESUME_FAILED`
 * `RESUME_IN_PROGRESS`
 * `RESUME_TARGET_LOST`
+* `ROLE_NOT_FOUND`
 * `ROLLED_BACK`
 * `ROUTE_NOT_FOUND`
 * `RULE_DEFINE_FAILED`
diff --git a/content/docs/references/api/error-code-ledger.mdx b/content/docs/references/api/error-code-ledger.mdx
index af0915a155b..7194045bbf2 100644
--- a/content/docs/references/api/error-code-ledger.mdx
+++ b/content/docs/references/api/error-code-ledger.mdx
@@ -478,6 +478,7 @@ const result = ErrorCode.parse(data);
 * `RESUME_FAILED`
 * `RESUME_IN_PROGRESS`
 * `RESUME_TARGET_LOST`
+* `ROLE_NOT_FOUND`
 * `ROLLED_BACK`
 * `ROUTE_NOT_FOUND`
 * `RULE_DEFINE_FAILED`
diff --git a/packages/plugins/plugin-auth/src/accept-invitation-adopt-membership.test.ts b/packages/plugins/plugin-auth/src/accept-invitation-adopt-membership.test.ts
index 51bad787eb2..553e3661ead 100644
--- a/packages/plugins/plugin-auth/src/accept-invitation-adopt-membership.test.ts
+++ b/packages/plugins/plugin-auth/src/accept-invitation-adopt-membership.test.ts
@@ -448,3 +448,70 @@ describe('#7725 — the delegated-admin issuance scope is UNCHANGED (ADR-0090 D1
     expect(invitationsFor(engine, 'scoped.denied@example.com')).toHaveLength(0);
   });
 });
+
+describe('#24750 — invite-member refuses an unknown role with the ADR-0112 code ROLE_NOT_FOUND', () => {
+  // The spec's invitation `role` docstring (`identity/organization.zod.ts`)
+  // promises "refused at the door (`ROLE_NOT_FOUND`) before any invitation row
+  // exists". better-auth's invite route throws that refusal with a message and
+  // no `code`; `update-member-role` throws the same refusal WITH one. These pin
+  // the door's answer, the untouched valid-role path, and the control door.
+  beforeEach(() => {
+    vi.spyOn(console, 'info').mockImplementation(() => {});
+    vi.spyOn(console, 'warn').mockImplementation(() => {});
+  });
+
+  afterEach(() => {
+    vi.restoreAllMocks();
+  });
+
+  it('an unknown role is refused 400 with code ROLE_NOT_FOUND, the message names the role, and no invitation row exists', async () => {
+    const { engine, manager, owner } = await bootWithOwner();
+
+    const res = await post(
+      manager,
+      '/organization/invite-member',
+      { email: 'qa-invitee@example.com', role: 'no_such_role', organizationId: DEFAULT_ORG },
+      owner.cookie,
+    );
+    expect(res.status).toBe(400);
+    const body: any = await res.json();
+    expect(body.code).toBe('ROLE_NOT_FOUND');
+    expect(body.message).toContain('no_such_role');
+    expect(invitationsFor(engine, 'qa-invitee@example.com')).toHaveLength(0);
+  });
+
+  it('CONTROL: a valid role is unchanged — 200 and one pending row carrying that role', async () => {
+    const { engine, manager, owner } = await bootWithOwner();
+
+    const res = await post(
+      manager,
+      '/organization/invite-member',
+      { email: 'qa-valid@example.com', role: 'member', organizationId: DEFAULT_ORG },
+      owner.cookie,
+    );
+    expect(res.status, await res.clone().text()).toBe(200);
+    const rows = invitationsFor(engine, 'qa-valid@example.com');
+    expect(rows).toHaveLength(1);
+    expect(rows[0]!.status).toBe('pending');
+    expect(rows[0]!.role).toBe('member');
+  });
+
+  it('CONTROL: update-member-role keeps the code it already answered with — 400 ROLE_NOT_FOUND, role unchanged', async () => {
+    const { engine, manager, owner } = await bootWithOwner();
+    const colleague = await signUp(manager, engine, 'colleague@example.com');
+    const [membership] = membersOf(engine, DEFAULT_ORG, colleague.userId);
+    expect(membership, 'the reconciler did not bind the colleague').toBeDefined();
+
+    const res = await post(
+      manager,
+      '/organization/update-member-role',
+      { memberId: String(membership!.id), role: 'no_such_role', organizationId: DEFAULT_ORG },
+      owner.cookie,
+    );
+    expect(res.status).toBe(400);
+    const body: any = await res.json();
+    expect(body.code).toBe('ROLE_NOT_FOUND');
+    expect(body.message).toContain('no_such_role');
+    expect(membersOf(engine, DEFAULT_ORG, colleague.userId)[0]!.role).toBe('member');
+  });
+});
diff --git a/packages/plugins/plugin-auth/src/auth-manager.ts b/packages/plugins/plugin-auth/src/auth-manager.ts
index 886ff6a119e..658b4666de2 100644
--- a/packages/plugins/plugin-auth/src/auth-manager.ts
+++ b/packages/plugins/plugin-auth/src/auth-manager.ts
@@ -105,6 +105,7 @@ import {
 } from './impersonation-bearer-rotation.js';
 import { echoInstalledSessionToken } from './two-factor-rotated-token-echo.js';
 import { resetVerifiedOnTwoFactorReenrollment } from './two-factor-reenrollment-verified-reset.js';
+import { codeInviteRoleNotFound } from './invite-role-not-found-code.js';
 import { attachSessionToCredentialResponse } from './session-envelope-completion.js';
 import {
   applyPlatformAdminImpersonation,
@@ -2970,6 +2971,12 @@ export class AuthManager {
             return;
           }
 
+          // ── #24750: invite-member's unknown-role refusal carries its code ──
+          // better-auth throws it with only a message; the spec promises
+          // `ROLE_NOT_FOUND` (see `invite-role-not-found-code.ts`). It throws
+          // on a match, so it stays after every section above.
+          await codeInviteRoleNotFound(ctx);
+
           if (ctx?.path !== '/sign-up/email') return;
           // ADR-0069 D1 — stamp password_changed_at for a newly-created local
           // user (expiry clock starts at sign-up). Best-effort.
diff --git a/packages/plugins/plugin-auth/src/invite-role-not-found-code.ts b/packages/plugins/plugin-auth/src/invite-role-not-found-code.ts
new file mode 100644
index 00000000000..cb8a65dc5ed
--- /dev/null
+++ b/packages/plugins/plugin-auth/src/invite-role-not-found-code.ts
@@ -0,0 +1,68 @@
+// Copyright (c) 2026 ObjectStack. Licensed under the Apache-2.0 license.
+
+/**
+ * #24750 — `POST /organization/invite-member` refused a role outside the
+ * closed membership vocabulary with a message and no `code`.
+ *
+ * ## The defect, at the seam
+ *
+ * better-auth's invite route checks the requested role against the static
+ * roles (plus the organization's dynamic ones, when dynamic access control is
+ * on) and throws
+ *
+ *     new APIError("BAD_REQUEST", { message: `${ROLE_NOT_FOUND}: ${unknownRoles}` })
+ *
+ * (`dist/plugins/organization/routes/crud-invites.mjs`, measured against the
+ * installed better-auth `1.7.3`). Its sibling `update-member-role`
+ * (`routes/crud-members.mjs`) throws the SAME refusal with
+ * `code: ROLE_NOT_FOUND` beside the identical message — so one vendor
+ * condition reached the wire coded on one door and uncoded on the other. The
+ * spec promises the code on this door: the invitation schema's `role`
+ * docstring (`identity/organization.zod.ts`) says a name outside the
+ * vocabulary is "refused at the door (`ROLE_NOT_FOUND`) before any invitation
+ * row exists", and an ADR-0112 client branches on `error.code`, never on prose.
+ *
+ * ## What this does
+ *
+ * Runs in the `after` hook, where better-auth hands the thrown `APIError` over
+ * on `ctx.context.returned`, and re-throws THIS refusal — and only this one —
+ * as `APIError('BAD_REQUEST', { code: 'ROLE_NOT_FOUND', message })` with the
+ * vendor's own message, so the body is byte-for-byte what `update-member-role`
+ * answers for the same condition. better-auth's hook runner replaces the
+ * returned value with an `APIError` an after hook throws, so the status, the
+ * message and the moment of the refusal (before any invitation row is written)
+ * are the vendor's; only the missing `code` is added.
+ *
+ * Recognition is deliberately narrow: the invite path, a 400 `APIError`, no
+ * `code` of its own, and a message that starts with the vendor's
+ * `ROLE_NOT_FOUND: ` prefix. Every other refusal on the route — including any
+ * future vendor release that codes this one itself — passes through untouched.
+ * The vendored library is not patched.
+ */
+
+/** The published endpoint whose refusal this codes. */
+export const INVITE_MEMBER_PATH = '/organization/invite-member';
+
+/** The ADR-0112 code the spec's invitation `role` docstring promises. */
+export const ROLE_NOT_FOUND_CODE = 'ROLE_NOT_FOUND';
+
+/** better-auth's message prefix for this refusal: `ROLE_NOT_FOUND: <roles>`. */
+const VENDOR_MESSAGE_PREFIX = `${ROLE_NOT_FOUND_CODE}: `;
+
+/**
+ * Re-throw invite-member's uncoded unknown-role refusal with
+ * `code: 'ROLE_NOT_FOUND'`. A no-op on every other path and every other
+ * answer. Call it LAST in the `after` hook: the throw ends the hook.
+ */
+export async function codeInviteRoleNotFound(ctx: any): Promise<void> {
+  if (ctx?.path !== INVITE_MEMBER_PATH) return;
+  const returned = ctx?.context?.returned;
+  const { APIError, isAPIError } = await import('better-auth/api');
+  if (!isAPIError(returned)) return;
+  if (returned.statusCode !== 400) return;
+  const body = returned.body as { code?: unknown; message?: unknown } | undefined;
+  if (body?.code !== undefined) return;
+  const message = body?.message;
+  if (typeof message !== 'string' || !message.startsWith(VENDOR_MESSAGE_PREFIX)) return;
+  throw new APIError('BAD_REQUEST', { code: ROLE_NOT_FOUND_CODE, message });
+}
diff --git a/packages/spec/src/api/error-code-ledger.zod.ts b/packages/spec/src/api/error-code-ledger.zod.ts
index c1463e2555f..bce4082daca 100644
--- a/packages/spec/src/api/error-code-ledger.zod.ts
+++ b/packages/spec/src/api/error-code-ledger.zod.ts
@@ -604,6 +604,7 @@ export const ERROR_CODE_LEDGER = {
     'PASSWORD_REUSE',
     'OAUTH_REGISTER_FAILED',       // better-auth rejected the client registration
     'PHONE_NOT_ENABLED',
+    'ROLE_NOT_FOUND',             // [#24750] 400 on /organization/invite-member and /organization/update-member-role: the requested membership role is outside the closed vocabulary, refused before any invitation or membership row is written; better-auth's code, stamped by plugin-auth on the invite door (`invite-role-not-found-code.ts`), pass-through from better-auth on update-member-role
     'SAML_REGISTER_FAILED',
     'SELF_REGISTRATION_CLOSED',   // [#11739] audience posture invite_only: self-registration is closed (no pending invitation for this address)
     'SSO_REGISTER_FAILED',