The error for me was:
Manifest merger failed : Attribute meta-data#android.support.VERSION@value value=(26.0.2) from [com.android.support:percent:26.0.2] AndroidManifest.xml:25:13-35
is also present at [com.android.support:support-v4:26.1.0] AndroidManifest.xml:28:13-35 value=(26.1.0).
Suggestion: add 'tools:replace="android:value"' to <meta-data> element at AndroidManifest.xml:23:9-25:38 to override.
The solution for me was in my project Gradle file I needed to bump my com.google.gms:google-services version.
I was using version 3.1.1:
classpath 'com.google.gms:google-services:3.1.1
And the error resolved after I bumped it to version 3.2.1:
classpath 'com.google.gms:google-services:3.2.1
I had just upgraded all my libraries to the latest including v27.1.1 of all the support libraries and v15.0.0 of all the Firebase libraries when I saw the error.