I think maybe the Gandi API endpoint has changed, not sure if the API requests stay the same or not. I'm seeing reported errors like {"object": "HTTPNotFound", "cause": "Not Found", "code": 404, "message": "The resource could not be found."} when trying to add TXT records. I don't personally have access to a Gandi account, this is based on second hand info so I'm just flagging it in case anyone else is seeing this.

https://api.gandi.net/docs/livedns/