Why can't I get json object without force=True attribute?

Question

Flask

Today I started testing the restplus framework for flask.
Faced with the fact that I can not correctly get the json object I need after the post request.
api.payload does not work, namely it returns None.
Also, I can't use the request.get_json() method without the force = True attribute.
i.e. I can get data only using a method like this request.get_json(force=True) and nothing else.
Why is this happening?