I want to send a POST request with a body in WSO2. actually, I have a Django rest framework with some APIs and want to send requests in WSO2 API manager. it's all OK for GET, DELETE but when I want to POST some request I'll receive a bad request from Django server.
Django server is running on http://localhost:8000/user-api/users/
in wso2 api publisher api's URL is : http://localhost:8243/users/1.0.0
endpoint in wso2 is : http://localhost:8000/user-api/users/
the below picture is what I receive when I send GET request:

I send POST request with this json as body:

and here is what I receive when I send POST request:

Everything is ok when I check the server's URL in my browser.
UPDATE:
when I use my Django server as a gateway for WSO2 everything is OK but when I use default WSO2-Gateway everything goes wrong.