Here is one of the best references I’ve found for creating ORDS REST services with PL/SQL.
There are examples of the various methods (GET, POST, PUT, DELETE), as well as examples for authentication.
One thing to note is that REST modules created with PL/SQL are separate from those created in APEX. Therefore, modules created in APEX cannot be edited with PLSQL.
Creating REST modules in PL/SQL is the more robust method, as it allows you to customize it better. Also, having any sort of logic inside stored procedures and database objects is always a good idea.