## Context
When a trialing workspace (trial without a credit card) clicks **Add
Credit Card** from the "End trial period" banner or the AI-chat
usage-limit banner, the modal currently redirects the browser to
Stripe's hosted billing portal to collect the card. Since we already
embed the Stripe Payment Element in onboarding, this brings the same
in-app experience to the trial-end modal so the whole flow stays inside
Twenty.
## Why the onboarding flow couldn't be reused as-is
The onboarding embed (`createSubscriptionPaymentIntent` /
`SubscriptionPaymentForm`) **creates a new subscription** with
`payment_behavior: 'default_incomplete'`. In the trial-end case the
customer **already has a trialing subscription**, so that path throws
`BILLING_SUBSCRIPTION_INVALID`. The correct primitive here is a
**SetupIntent** against the existing customer: collect + save the card,
then end the trial.
A standalone SetupIntent attaches the card to the customer but does
**not** make it the default (the Stripe portal used to do that for us),
so the trial-end invoice would have no payment method. The backend now
backfills the customer default before charging.
## Changes
**Backend**
- `StripeCustomerService`: `createSetupIntent()` for an existing
customer, and `ensureDefaultPaymentMethod()` which sets the customer
default only when none is already set (won't clobber a portal-chosen
default).
- `BillingPortalWorkspaceService.createPaymentMethodSetupIntent()`:
returns a SetupIntent client secret for the current non-canceled
subscription's customer.
- `BillingSubscriptionService.endTrialPeriod()`: ensures a default
payment method before `trial_end: 'now'`.
- New `createBillingPaymentMethodSetupIntent` mutation +
`BillingSetupIntent` DTO; SDK schema snapshot synced.
**Frontend**
- `AddPaymentMethodForm`: Stripe Elements (`mode: 'setup'`), confirms
with `redirect: 'if_required'` so the common card case stays in-app; 3DS
still redirects and is finished by the existing
`EndTrialAfterPaymentMethodEffect`.
- `AddCreditCardModal`: hosts the embedded form.
- Both trial-end banners (`InformationBannerEndTrialPeriod`,
`AIChatNoMoreBillingCreditsBanner`) open the embedded modal instead of
redirecting when no card is on file; the AI-chat path preserves its
thread context in the 3DS return URL.
## Flow
1. User clicks **Add Credit Card** → embedded modal opens.
2. Card entered → `createBillingPaymentMethodSetupIntent` →
`confirmSetup({ redirect: 'if_required' })`.
3. Non-3DS: confirms inline → `endSubscriptionTrialPeriod` →
subscription active, no redirect.
4. 3DS: redirects to `?startSubscriptionAfterPaymentMethod=true` →
existing effect finishes activation.
5. Self-hosted instances without a Stripe publishable key fall back to
the existing portal redirect (the form renders an unavailable state).
## Notes for reviewers
- The metadata GraphQL types were regenerated by hand (codegen needs a
live `/metadata` server, which wasn't available in the authoring
environment); a `graphql:generate --configuration=metadata` run against
a live backend should be a no-op.
- Local `typecheck`/`lint` could not be run in the authoring environment
(dependency install was blocked); relying on CI to validate.
- Scope is intentionally limited to the two trial-end banner modals. The
Settings → Billing "update payment method" link still uses the Stripe
portal.
https://claude.ai/code/session_01VU7SfrSgaYWr2AhVL8DMfu
---
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Félix Malfait
94dbcc27a9
