post
https://apibeta.familysearch.org/platform/tree/couple-relationships/
Add or update specific facts attached to a couple. FamilySearch also allows you to update the persons in a couple relationship.
201The successful update contained a single conclusion. Expect the id of the conclusion in the 'Location' header.
204The update was successful.
404If the requested relationship is not found.
410If the requested relationship has been deleted or merged.
429The request was throttled.