Hi Jeremie, I have just tried posting a score in a loaderboard from Kindle HDX 8.9 through the latest version of GameCircle plugin released in Asset Store. Version: 2.4.0 (Mar 02, 2014) Size: 14.2 MB I did not face any issue. The version has been updated very recently with couple of fixes in Asset Store. Can you please update your plugin and try? Thank you for reaching out.