Hi, @yorambaron.
I’m not proficient enough with Java to identify the issue in your code, but I’m seeing examples out there with both of these headers:
"content-type", "multipart/form-data; boundary=----WebKitFormBoundary7MA4YWxkTrZu0gW"
"Content-Type", "application/x-www-form-urlencoded"
Could you try with these?