Android : Social.ReportProgress method with Google Play Games Plugin returns always false

I ran into an issue with the Google Play Games Plugin provided by Google for the Unity3D editor. I've just included the plugin in my unity project and when I put the app build on my android device, I can sign in the Google Play Games with my Google account. However, my achievements are never modified on line because the callback of the method Social.ReportProgress returns always "false". (the bool success)

// unlock achievement (achievement ID "Cfjewijawiu_QA")
Social.ReportProgress("Cfjewijawiu_QA", 100.0f, (bool success) => {
  // handle success or failure
});

I've checked that I use the correct ID for my achivements. The difference between my code and this official piece of code provided by Google on github is the percentage. For instance, my app can put "33.3333" for the percentage. When I tried to put the same percentage on the method (100.0f), the bool success was also false. What is wrong ?