Problem Identification:
There is a conflict in the libraries version, you use 'com.google.android.gms:play-services-auth:11.6.0' , and the latest version is now , which requires compatible compileSdkVersion and targetSdkVersion
Why did this happen?:
Compiling lib contains a higher level of api than the level of your api application.
Decision:
Download compileSdkVersion and targetSdkVersion in the latest version (now it's 27 ) , and your com.android.support also compatible with all applications and libraries.
You should also add google() to your repositories:
repositories { jcenter() google() } ......... allprojects { repositories { jcenter() google() } }
Note: updating targetSdkVersion not required for this problem, but it is better to use the application to target a wide range of devices.
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