FeignClient not sending proper form url encoded request

We have a scenario where a POST application/form-url-encoded request is to be sent to an API endpoint. And we are using @FeignClient annotated interface having a @PostMapping annotated function which takes in a POJO class as an argument such that the attributes of the class will be set as key value pairs of form data.

The issue is that the POJO class ( which is an argument to the function ) is derived from a base class. Due to which the form data posted to the API endpoint does not contain the attributes of the base class.

It works fine if the argument to @PostMapping function is a simple POJO class which doesn't extend any other class.

Can you please suggest a solution to the issue?

Start by reproducing the form-url-encoded POST through the @FeignClient and @PostMapping scenario described, comparing a simple POJO with one that extends a base class. Trace how the POJO is converted into form key-value pairs; done means inherited attributes are included in the request while existing simple-POJO behavior remains intact.