diff --git a/modules/billing/migrations/20260707100000-backfill-missing-signup-grant-credits.js b/modules/billing/migrations/20260707100000-backfill-missing-signup-grant-credits.js
new file mode 100644
index 000000000..7c261c07f
--- /dev/null
+++ b/modules/billing/migrations/20260707100000-backfill-missing-signup-grant-credits.js
@@ -0,0 +1,97 @@
+/**
+ * Migration: Backfill the one-shot signupGrant to plan orgs created without it.
+ *
+ * The signupGrant was historically credited only on the invite/verify
+ * org-creation path (organizations.service.js::createOrganizationForUser). The
+ * generic path behind POST /api/organizations (organizations.crud.service.js)
+ * never credited it, so orgs created that way — e.g. via a manual "create
+ * workspace" screen — started at 0 balance. The code gap is fixed alongside
+ * this migration; this repairs already-affected orgs.
+ *
+ * Delegates to BillingSignupGrantService.grantOnSignup per org so it goes
+ * through the EXACT runtime grant path rather than re-implementing the ledger
+ * write. That reuse is deliberate — it inherits, for free and consistently:
+ *   - ObjectId casting: the repository writes via the Mongoose model, whose
+ *     `organization` field is Schema.ObjectId, so the string orgId is cast to a
+ *     real ObjectId (a raw-driver write keyed on a string would create orphan,
+ *     app-invisible documents that never match existing ones).
+ *   - the plan-definition co-presence guard (BillingPlanService.getActivePlan
+ *     refuses a signupGrant configured without oneShot).
+ *   - Zod amount validation (creditGrant → ExtraBalanceCreditGrant.parse).
+ *   - idempotency via the synthetic refId `signup_grant-<orgId>`, so an org
+ *     already credited (at signup, by the earlier 20260511 backfill, or by a
+ *     prior run of this one) is a no-op.
+ *
+ * Config-driven: only orgs on a plan that defines a positive signupGrant are
+ * touched; a project that configures none is a no-op. This generalises the
+ * earlier 20260511 backfill, which hardcoded 500 and enumerated the
+ * `subscriptions` collection (missing free orgs with no subscription document);
+ * this one enumerates the `organizations` collection.
+ *
+ * Safe to run while the app is live: each grant is a single-document atomic
+ * ledger push and the migration runner serialises execution via a DB-level claim.
+ */
+import mongoose from 'mongoose';
+import config from '../../../config/index.js';
+import BillingSignupGrantService from '../services/billing.signupGrant.service.js';
+
+/**
+ * @returns {Promise<void>}
+ */
+export async function up() {
+  // Plans that define a positive signupGrant — the only orgs worth scanning.
+  const grantPlanIds = (config?.billing?.planDefinitions ?? [])
+    .filter((def) => def?.planId && typeof def.signupGrant === 'number' && def.signupGrant > 0)
+    .map((def) => def.planId);
+
+  if (grantPlanIds.length === 0) {
+    console.info('[migration] backfill-signup-grant: no plan defines a signupGrant — nothing to do');
+    return;
+  }
+
+  const organizations = mongoose.connection.db.collection('organizations');
+  const cursor = organizations.find(
+    { plan: { $in: grantPlanIds } },
+    { projection: { _id: 1, plan: 1 } },
+  );
+
+  let granted = 0;
+  let skipped = 0;
+  let failed = 0;
+
+  for await (const org of cursor) {
+    // grantOnSignup is idempotent (refId) and never throws — reuses the runtime
+    // path so ObjectId casting + validation + co-presence guard all apply.
+    const result = await BillingSignupGrantService.grantOnSignup({
+      orgId: org._id.toString(),
+      planId: org.plan,
+    });
+
+    if (result == null) {
+      // Plan has no exposed grant (co-presence guard) or a swallowed error — logged by the service.
+      failed += 1;
+    } else if (result.applied === false) {
+      // Idempotent no-op — org already had a signup_grant entry.
+      skipped += 1;
+    } else {
+      granted += 1;
+    }
+  }
+
+  console.info(`[migration] backfill-signup-grant: complete — granted=${granted} skipped=${skipped} failed=${failed}`);
+}
+
+/**
+ * Reverse: intentional no-op.
+ *
+ * This migration shares the `signup_grant` refId scheme with the app's runtime
+ * grant and the earlier 20260511 backfill, so signup_grant ledger entries cannot
+ * be attributed to this migration specifically. A blanket removal would revert
+ * legitimately-earned grants too. Reverting is left to a manual, audited
+ * operation if ever required.
+ *
+ * @returns {Promise<void>}
+ */
+export async function down() {
+  console.warn('[migration] backfill-signup-grant DOWN: intentional no-op — signup_grant entries are not attributable to this migration; revert manually if required.');
+}
diff --git a/modules/billing/tests/billing.migration.backfill-signup-grant.integration.tests.js b/modules/billing/tests/billing.migration.backfill-signup-grant.integration.tests.js
new file mode 100644
index 000000000..0c35a487d
--- /dev/null
+++ b/modules/billing/tests/billing.migration.backfill-signup-grant.integration.tests.js
@@ -0,0 +1,104 @@
+/**
+ * Module dependencies.
+ */
+import mongoose from 'mongoose';
+import { describe, beforeAll, afterEach, afterAll, test, expect } from '@jest/globals';
+
+import mongooseService from '../../../lib/services/mongoose.js';
+import config from '../../../config/index.js';
+import { up as backfillSignupGrants } from '../migrations/20260707100000-backfill-missing-signup-grant-credits.js';
+
+/**
+ * Integration tests for the signup-grant backfill migration.
+ *
+ * Regression guard for the string-vs-ObjectId bug: billingextrabalances.organization
+ * is Schema.ObjectId, so the migration MUST credit orgs through a path that casts to
+ * ObjectId (it delegates to grantOnSignup → the Mongoose repository) — a raw-driver
+ * write keyed on a string would create orphan, app-invisible ghost documents.
+ */
+describe('backfill-missing-signup-grant migration (integration):', () => {
+  let organizations;
+  let extraBalances;
+  let grantPlanId;
+  let grantAmount;
+  let createdOrgIds = [];
+
+  /**
+   * Seed an organization on the given plan and track it for cleanup.
+   * @param {string} plan - The plan id to set on the org.
+   * @returns {Promise<import('mongoose').Types.ObjectId>} The new org ObjectId.
+   */
+  const seedOrg = async (plan) => {
+    const _id = new mongoose.Types.ObjectId();
+    await organizations.insertOne({ _id, name: `IT ${_id.toString()}`, plan });
+    createdOrgIds.push(_id);
+    return _id;
+  };
+
+  beforeAll(async () => {
+    await mongooseService.loadModels();
+    await mongooseService.connect();
+    organizations = mongoose.connection.db.collection('organizations');
+    extraBalances = mongoose.connection.db.collection('billingextrabalances');
+    const def = (config?.billing?.planDefinitions ?? []).find(
+      (d) => typeof d.signupGrant === 'number' && d.signupGrant > 0,
+    );
+    grantPlanId = def.planId;
+    grantAmount = def.signupGrant;
+  });
+
+  afterEach(async () => {
+    if (createdOrgIds.length) {
+      await organizations.deleteMany({ _id: { $in: createdOrgIds } });
+      await extraBalances.deleteMany({ organization: { $in: createdOrgIds } });
+      createdOrgIds = [];
+    }
+  });
+
+  afterAll(async () => {
+    await mongooseService.disconnect();
+  });
+
+  test('credits the configured grant to an ObjectId-keyed org missing it, readable by ObjectId', async () => {
+    const orgId = await seedOrg(grantPlanId);
+
+    await backfillSignupGrants();
+
+    // Stored + readable keyed on the ObjectId — the critical-fix assertion.
+    const eb = await extraBalances.findOne({ organization: orgId });
+    expect(eb).not.toBeNull();
+    expect(eb.cachedBalance).toBe(grantAmount);
+    const grant = (eb.ledger || []).find((e) => e.source === 'signup_grant');
+    expect(grant).toBeDefined();
+    expect(grant.amount).toBe(grantAmount);
+    expect(grant.refId).toBe(`signup_grant-${orgId.toString()}`);
+    // A string-keyed lookup must NOT find a duplicate ghost document.
+    expect(await extraBalances.findOne({ organization: orgId.toString() })).toBeNull();
+  });
+
+  test('is idempotent — a second run does not double-credit', async () => {
+    const orgId = await seedOrg(grantPlanId);
+
+    await backfillSignupGrants();
+    await backfillSignupGrants();
+
+    const docs = await extraBalances.find({ organization: orgId }).toArray();
+    expect(docs).toHaveLength(1);
+    expect(docs[0].cachedBalance).toBe(grantAmount);
+    const grants = (docs[0].ledger || []).filter((e) => e.source === 'signup_grant');
+    expect(grants).toHaveLength(1);
+  });
+
+  test('skips an org that already holds a signup_grant entry', async () => {
+    const orgId = await seedOrg(grantPlanId);
+    const repo = (await import('../repositories/billing.extraBalance.repository.js')).default;
+    await repo.creditGrant(orgId.toString(), grantAmount, 'signup_grant');
+
+    await backfillSignupGrants();
+
+    const docs = await extraBalances.find({ organization: orgId }).toArray();
+    expect(docs).toHaveLength(1);
+    const grants = (docs[0].ledger || []).filter((e) => e.source === 'signup_grant');
+    expect(grants).toHaveLength(1);
+  });
+});
diff --git a/modules/organizations/services/organizations.crud.service.js b/modules/organizations/services/organizations.crud.service.js
index bf6ea955b..9f109b1e9 100644
--- a/modules/organizations/services/organizations.crud.service.js
+++ b/modules/organizations/services/organizations.crud.service.js
@@ -23,6 +23,7 @@ const normalizeDomain = (value = '') => value.trim().toLowerCase();
 import OrganizationsRepository from '../repositories/organizations.repository.js';
 import MembershipRepository from '../repositories/organizations.membership.repository.js';
 import UserService from '../../users/services/users.service.js';
+import BillingSignupGrantService from '../../billing/services/billing.signupGrant.service.js';
 import { slugify } from '../helpers/organizations.slug.js';
 import { MEMBERSHIP_STATUSES, MEMBERSHIP_ROLES } from '../lib/constants.js';
 import { runOrganizationRemovedHandlers } from '../lib/orgRemoval.registry.js';
@@ -120,6 +121,14 @@ const create = async (body, user) => {
     throw err;
   }
 
+  // Best-effort signup grant — mirrors organizations.service.js::createOrganizationForUser.
+  // Every org-creation path (including this generic one behind POST /api/organizations)
+  // must credit the configured one-shot signupGrant, else a fresh org on a plan that
+  // defines one starts at 0 balance. Called outside the rollback try/catch so a billing
+  // failure never rolls back the org; grantOnSignup never throws and is idempotent
+  // (refId signup_grant-<orgId>). No-op when the plan defines no signupGrant.
+  await BillingSignupGrantService.grantOnSignup({ orgId: result._id.toString(), planId: result.plan || 'free' });
+
   return result;
 };
 
diff --git a/modules/organizations/tests/organizations.crud.grant.unit.tests.js b/modules/organizations/tests/organizations.crud.grant.unit.tests.js
new file mode 100644
index 000000000..aa747a07d
--- /dev/null
+++ b/modules/organizations/tests/organizations.crud.grant.unit.tests.js
@@ -0,0 +1,97 @@
+/**
+ * Module dependencies.
+ */
+import { jest, describe, test, expect, beforeEach } from '@jest/globals';
+
+/**
+ * Unit tests — verify organizations.crud.service.create() credits the one-shot
+ * signup grant on the generic POST /api/organizations path, mirroring the
+ * invite/verify path (organizations.service.js::createOrganizationForUser). A
+ * fresh org on a plan that defines a signupGrant must not start at 0 balance.
+ */
+
+const mockGrantOnSignup = jest.fn().mockResolvedValue({ applied: true });
+jest.unstable_mockModule('../../billing/services/billing.signupGrant.service.js', () => ({
+  default: { grantOnSignup: mockGrantOnSignup },
+}));
+
+const mockOrgCreate = jest.fn().mockResolvedValue({ _id: 'org1', plan: 'free' });
+const mockOrgRemove = jest.fn().mockResolvedValue({});
+jest.unstable_mockModule('../repositories/organizations.repository.js', () => ({
+  default: {
+    create: mockOrgCreate,
+    findOne: jest.fn().mockResolvedValue(null),
+    remove: mockOrgRemove,
+    list: jest.fn().mockResolvedValue([]),
+    update: jest.fn(),
+    get: jest.fn(),
+    exists: jest.fn().mockResolvedValue(false),
+  },
+}));
+
+const mockMembershipCreate = jest.fn().mockResolvedValue({ _id: 'm1' });
+jest.unstable_mockModule('../repositories/organizations.membership.repository.js', () => ({
+  default: {
+    create: mockMembershipCreate,
+    deleteMany: jest.fn(),
+    list: jest.fn().mockResolvedValue([]),
+    findOne: jest.fn().mockResolvedValue(null),
+    update: jest.fn(),
+    remove: jest.fn(),
+    count: jest.fn(),
+  },
+}));
+
+jest.unstable_mockModule('../../users/services/users.service.js', () => ({
+  default: {
+    updateById: jest.fn().mockResolvedValue({}),
+    findWithFilter: jest.fn().mockResolvedValue([]),
+    getBrut: jest.fn(),
+  },
+}));
+
+jest.unstable_mockModule('../../../lib/helpers/emailVerification.js', () => ({
+  assertEmailVerified: jest.fn(),
+}));
+
+jest.unstable_mockModule('../../../lib/services/logger.js', () => ({
+  default: { error: jest.fn(), warn: jest.fn(), info: jest.fn() },
+}));
+
+jest.unstable_mockModule('../../../config/index.js', () => ({
+  default: { organizations: { enabled: false } },
+}));
+
+const { default: OrgCrudService } = await import('../services/organizations.crud.service.js');
+
+describe('organizations.crud.service.create signup grant:', () => {
+  beforeEach(() => {
+    mockGrantOnSignup.mockClear();
+    mockOrgCreate.mockResolvedValue({ _id: 'org1', plan: 'free' });
+  });
+
+  test('credits the one-shot signup grant for the freshly created org', async () => {
+    const user = { id: 'u1', _id: 'u1', email: 'a@b.com', emailVerified: true };
+    const result = await OrgCrudService.create({ name: 'Test Org' }, user);
+
+    expect(result).toEqual({ _id: 'org1', plan: 'free' });
+    expect(mockGrantOnSignup).toHaveBeenCalledTimes(1);
+    expect(mockGrantOnSignup).toHaveBeenCalledWith({ orgId: 'org1', planId: 'free' });
+  });
+
+  test('defaults planId to free when the created org has no plan field', async () => {
+    mockOrgCreate.mockResolvedValueOnce({ _id: 'org2' });
+    const user = { id: 'u1', _id: 'u1', email: 'a@b.com', emailVerified: true };
+    await OrgCrudService.create({ name: 'No Plan Org' }, user);
+
+    expect(mockGrantOnSignup).toHaveBeenCalledWith({ orgId: 'org2', planId: 'free' });
+  });
+
+  test('does not credit the grant when membership creation fails (rollback exits before the grant)', async () => {
+    mockMembershipCreate.mockRejectedValueOnce(new Error('membership boom'));
+    const user = { id: 'u1', _id: 'u1', email: 'a@b.com', emailVerified: true };
+
+    await expect(OrgCrudService.create({ name: 'Rollback Org' }, user)).rejects.toThrow();
+    expect(mockGrantOnSignup).not.toHaveBeenCalled();
+  });
+});