An email or customer ID on file elsewhere no longer reaches that customer (2026-11-05)
Create or link a Customer and Convert one Lead make a separate record for an email your company doesn't serve, and Create or update a Customer Relationship returns 404.
Org API, Create or link a Customer (POST /api/v1/customers) and Convert one Lead (POST /api/v1/leads/{id}/convert): an email held by a customer your company doesn't serve now creates a separate record holding only what you sent. Before, these calls linked the existing customer and returned its name and phone. Responses keep the same shape. The email you sent is in email, and created is true.
Org API, Create or update a Customer Relationship (POST /api/v1/customer-relationships): returns 404 with NOT_FOUND for a customer your company doesn't serve. Before, it created a relationship with any customer whose ID you sent. Updating a relationship you have, or restoring one you deleted, is unchanged. Request bodies are unchanged: no field is rejected or removed.
An email held by a customer your company already serves still reaches that customer. The two records join when the customer confirms through an emailed link a team member sends from the customer page. See Add a customer.