I did this:

  const response = await fetch(
    url,
    {
      method: 'POST',
      headers: {
        'Content-Type': 'application/json',
      },
      body: JSON.stringify(reqData),
    }
  );
  const resData: ApiResponse = await response.json();

then I parsed resData. The JSON in the response is still type checked but I don't have to fight anymore with the HTTP library. I can't remember what it was as it never made it into a commit.