Updating a project

PATCH /projects/{project_id} writes back the fields your ERP owns. The canonical use is reconciling identifiers: your ERP creates a project / commission number and PATCHes it into object_number so every later tender.completed / order.completed webhook and GET /projects lines up with your own key.

Writable fields (all optional): object_number, name, status, estimated_value, currency, submission_date, custom_fields.

If object_number is the only field you need to write, you can skip PATCH entirely and send it as the external_id of an acknowledgement instead — see Acknowledging a project.

Semantics:

• Partial. Send only what you change. An omitted field is left untouched; an explicit null clears that field. status is the one exception — it cannot be null (a project always has a lifecycle state), and an unknown status value is a 400.
• object_number is a grouping key. Mercura derives the master-project grouping from this value at read time, so writing it simply moves the one project row you addressed into (or out of) a group — sibling rows that shared the old value are not rewritten.
• custom_fields is label-keyed and shallow-merged. Use the same labels you receive on GET (and, for a multi-select, the same option labels). Keys you include are set; a key mapped to null clears that one field; keys you omit are left as they are. An unknown label — or an unknown option label on a multi-select — returns 400 VALIDATION_FAILED naming the offending keys, so a typo fails loudly instead of silently writing nothing.

Optimistic concurrency: read the project first, then echo the ETag you received as an If-Match header on the PATCH. If someone else changed the project in the meantime the ETag no longer matches and the request is rejected with 412 Precondition Failed — re-fetch and retry. Omit If-Match (or send If-Match: *) to skip the check. A no-op edit (an empty body, or values equal to the current ones) does not advance the project's updated_at.