Use standard HTTPException instead of hacking into JSONresponse.

this_api_response = Tools.createResponseOBJ(201, json_content=on_success_json)
                    else:
                        this_api_response = Tools.createResponseOBJ(400, {"status": "Failed", "message": "Cannot create user"})
 

raise HTTPException(status_code=400, detail="Cannot create user") # or provide dict in `detail` and it would be JSONed automatically