### Context
Several 'Customer not found' errors arrived in Sentry, all coming from
webhook-entitlement.service, at subscription creation (coinciding with
customer creation 99% of the time).
Stripe sends many events to update/create customer, subscription,
entitlement, ...
All these events are handle in parallel but customer.created stripe
event arrived first and few seconds after subscription.created and
entitlements.active_entitlement_summary.updated
Issue happens at entitlements.active_entitlement_summary.updated
handling. It checks for customer existence through subscription. But
subscription can be not created yet at this moment.
### Solution
Check directly for customer existence in billingCustomer table. Not sure
it will fix the error because of the parallel handling of Stripe event,
but should still be better.
### Tested
- Workspace creation
- Subscription upgrade (check for entitlement update)
closes https://github.com/twentyhq/twenty/issues/11960
52ad789e7a