AAPT: error: resource android:at

1、Open android/app project
2、Search this text androidx.core:core-ktx:+ into all solution
3、If you found this text in some dependency, change this androidx.core:core-ktx:+ for this androidx.core:core-ktx:1.6.0
4、Sync and run again
In my case, I had this problem with audioplayers: ^0.17.3 dependency. The + sign was causing the error.