Error Function code not defined for flow EWM RF Custom Application

Hello all, I am creating a custom RF application in SAP S/4HANA and I’m running into an issue where the screen is not rendering properly. I found a YouTube video suggesting this may happen when the PBO and PAI function modules have not been implemented yet, and in my case, that is true. Could someone please explain the correct way to build the PBO and PAI function modules for a custom RF screen?