The reason why the FDU request is not pushing through and update in PMS (or when error notification is received) could be due to:
The reservation screen/window on PMS is opened or locked by user (especially with Opera on-prem) which prevents any changes made to the reservation by external system. The reservation window should always be close before confirming/approving the FDU deal so that the update can be pushed into the specific reservation that was agreed by the guest.
The reservation has a "Checked-in" or "In-house" status. Once the reservation is checked-in in the PMS, room upgrade request through FDU is not possible as PMS does not allow room change when a room has been checked in, or the guest has already in-house. This is a logic within PMS to prevent discrepancies with the room occupancy and status, for example, to prevent double check-in for a room.
In case the guest requested to upgrade their room and the room is still available, front office can reverse check-in and request the room upgrade deal through Oaky FDU.