CRUD (GET, POST, PUT...) implementation / diagnosis in Flutter using REST API

I have a new project in Flutter where I have used REST API to handle data to/from the server. Some CRUD functionalities are working and some are not.

I want someone who is an expert in these basic data-related functionalities in the REST API environment to help me sort out and fix problems in CRUD functionalities (GET, POST, PUT etc.) from the flutter. for REST API, I am using the CUBA-PLATFORM REST API add-on which is basically a java-based tool.

Please contact me if you think can do this and are interested.