The write back functionality is covered in the FDMEE admin guide  in detail thus you may want to revisit to ensure you are fully clear on what Oracle supports out of the box. It is to a specify set of ERP versions and is based on the standard out of the box FDMEE direct ERP connection setup.

The general way to write back to non out of the box supported systems is to produce a flat file(Defined again in the FDMEE admin guide) and then load that flat file to your custom source system.

As always if there is functionality that you want that is not in the software go ahead and open an Oracle SR and log an enhancement request.

Question answered in first post based on the Oracle documentation reference.

Second your setup is only known by you not members on the board. All responses are based on the general information you provided.

Notably if you are asserting that the Oracle Engineers themselves specifically told you you can "directly write back to custom table using UDA"  then certainly they would provide you precise direction and/or updated FDMEE documentation reference on doing such.Oracle is the vendor not members on the board .

Also you may want to raise a documentation bug as that level of detail in terms of UDA write back does not appear to be laid out in the documentation.

Ensure you are looking at the most updated FDMEE admin guide. The updated admin guide even has a table showing the out of the box supported systems.

The FDMEE  admin guide(11.1.2.4.200) references direct integration write back rules for the standard direct erp out of the box connection setup.

As mentioned in the first post the approach to get data back to systems not under the standard FDMEE direct setup is the Write-back  available to a file-based source system. As always you can seek to build a custom process/routine to your system but of course that is up to you to define and setup.

Other experts may certainly provide their input.

Good luck and do let us know how you finalize.