@lxlvm thank you for your explanation. Indeed, OpenAPI file says to use application/x-www-form-urlencoded content type for a POST /notes request body, which is true, but it also supports application/json . We have this statement in docs (Requests)
We recommend using JSON body format when performing API requests. In order to do a proper JSON-formatted request, make sure you provide
Content-Type: application/jsonin HTTP request headers.
For thePOSTmethod, regular form-encoded body format is also supported but you may experience quirks related to lack of data types
but I agree, ideally, it should be reflected in OpenAPI file too.