You can download a test project from
http://www.mondoedp.com/uploads/media/irisftp/download/Test_ISAPI_DO64.zip

Delphi 10.2.3 - It needs IntraWEB 15.
In Unit3 you have to assign the correct connection parameters.

Project1SA is the stand-alone exe version that woeks fine.
ProjectISAPI is the IIS-dll version that can't connect with TOracleSession.

Note: for some reason FDConnection must be connected first then DOA, I didn't investigate but it doesn't matter in this case.