I received this error
i have full sdk intalled , 5.0.2 and 5.1.1 end all tools for build
Error:failed to find target android-21 : C:\Program Files\Android\Android Studio\gradle\m2repository\com\android\tools\sdk-common\24.2.2
<a href="install.android.platform">Install missing platform(s) and sync project</a>
after downloading the package that says, infinitely repeated the error
thanks for the support