fix(billing): send {} body on portal POST to satisfy Zod PortalRequest schema (#4137)

openPortal() was calling axios.post(url) with no body, causing Express/Zod
strict() to reject with "expected object, received undefined" (422). Passing
{} satisfies PortalRequest schema (returnUrl optional).

Author: PierreBrisorgueil

src/modules/billing/stores/billing.store.js

@@ -279,7 +279,7 @@ export const useBillingStore = defineStore('billing', {
       this.loading = true;
       try {
         const api = apiBase();
-        const res = await axios.post(`${api}/${config.api.endPoints.billing}/portal`);
+        const res = await axios.post(`${api}/${config.api.endPoints.billing}/portal`, {});
         const url = res?.data?.data?.url;
         if (!url) {
           throw new Error('Billing portal URL is missing from the API response');

src/modules/billing/tests/billing.store.unit.tests.js

@@ -258,6 +258,22 @@ describe('Billing Store', () => {
       expect(store.loading).toBe(false);
       spy.mockRestore();
     });
+
+    it('sends an empty object body to POST /portal (not undefined)', async () => {
+      const store = useBillingStore();
+      const portalUrl = 'https://billing.stripe.com/session/test_123';
+      axios.post.mockResolvedValueOnce({ data: { data: { url: portalUrl } } });
+      const originalLocation = window.location;
+      delete window.location;
+      window.location = { ...originalLocation, href: '' };
+      await store.openPortal();
+      // Second argument must be {} (empty object), not undefined
+      expect(axios.post).toHaveBeenCalledWith(
+        expect.stringContaining('/portal'),
+        {},
+      );
+      window.location = originalLocation;
+    });
   });
 
   describe('fetchUsageMeter', () => {