Kindly have a look of below mentioned learning path it will be useful for you.
https://academy.mendix.com/link/path/33/Create-a-REST-API-(Micro-Learning)-
Seems ok, what is the problem? Are you getting data?
Most easy way to find out is to set your response handling to “Store as a string" and show the string in a message
If you get data, you should go tthrough the entities by receiving them over association and then show them in a message, or form..
While creating JSON structure, use only objects you needed. While creating a import mapping select the entity already there (Persistant) rather than creating a new entity by studio pro based on the JSON. So that the data you import directly updates to the related entity, if you would like do before commit those changes, use an event handler and select before or after option commit to make changes to the data.