Create Agreement v6 API - SenderSigns LAST not working

I have been trying for ages to get the SenderSigns: "LAST" working correctly but doesnt seem to work.

If i add myself as a recieptient as participant 1 and then my customers as participant 2 and 3 (2 signers + myself) and set SenderSigns: "LAST" it doesnt work. I always get it first and the SenderSigns = "SEQUENTIAL" no matter what i try, can you let me know if there is anything else i need to do?

The sender MUST be the one who signs last as the agreement must be signed by the customers first and then finally signed by the sender to complete it.

This is using the POST /agreement API request for the v6 API.