Android – Gradle Sync Issue Kotlin after Android 3.1 Stable Update

You can solve this with one of the following solutions:

Update:

As of Android studio 3.0, it becomes much easier as it now shows a more helpful hint, so we only need to follow this hint.
for example:

All com.android.support libraries must use the exact same version specification (mixing versions can lead to runtime crashes). Found versions 27.0.2, 26.1.0. Examples include com.android.support:animated-vector-drawable:27.0.2 and com.android.support:customtabs:26.1.0

there are some combinations of libraries, or tools and libraries, that are incompatible, or can lead to bugs. One such incompatibility is compiling with a version of the Android support libraries that is not the latest version (or in particular, a version lower than your targetSdkVersion.)

Solution:
Add explicitly the library with the old version but with a new version number.
in my case com.android.support:customtabs:26.1.0 so I need to add:

implementation "com.android.support:customtabs:27.0.2"  

ie: Take the library from the second item, and implement it with the version number from the first.

Note: don't forget to press sync now so gradle can rebuild the dependency graph and see if there are any more conflicts.

Explanation:
you may be confused by the error message as don't use customtabs so how I have a conflict!!
well.. you didn't use it directly but one of your libraries uses an old version of customtabs internally, so you need to ask for it directly.

if you curious to know which of your libraries is responsible for the old version and maybe ask the author to update his lib, Run a Gradle dependency report, see the old answer to know how.

Note this

Old answer:

inspired by CommonsWare answer:

Run a Gradle dependency report to see what your full tree of dependencies is.

From there, you will see which one of your libraries are asking for a different version of the Android Support libraries. For whatever it is asking for, you can ask for it directly with the 25.2.0 version or use Gradle's other conflict resolution approaches to get the same versions.

Update:

As of gradle plugin version: 3.0 compile has been replaced by implementation or api see this answer for the difference.

hence use instead:

./gradlew -q dependencies app:dependencies --configuration debugAndroidTestCompileClasspath

or for windows cmd:

gradlew -q dependencies app:dependencies --configuration debugAndroidTestCompileClasspath

and search for the conflicted version.

For me, the error disappeared after removing com.google.android.gms:play-services:10.2.0

And only include com.google.android.gms:play-services-location:10.2.0 and com.google.android.gms:play-services-maps:10.2.0 as they are the only two play services that I use.

I think the gms:play-services depend on some old components of the support library, so we need to add them explicitly ourselves.

for AS 3.0 an older.

Run:

./gradlew -q dependencies <module-name>:dependencies --configuration implementation

Example:

./gradlew -q dependencies app:dependencies --configuration implementation

if someone knows a better way in the new gradle plugin please let me know.

You can update your Kotlin version in your project level build.gradle file. If you have it configured the usual way, you should have the following line in it around the top:

ext.kotlin_version = '1.1.2'

To upgrade to the version matching your plugin, simply change this line to:

ext.kotlin_version = '1.1.2-3'

Edit (to respond to a question below):

The error tells you that you need to upgrade your version, the question is where to find out that you have to put in 1.1.2-3 instead of saying, for example, 1.1.2-release-Studio2.3-3.

The best way to find out the latest version of Kotlin is by going to kotlinlang.org and looking for "Latest version". Should be right there on the front page.

Another thing to do if the version number is non-trivial like this is to check the repositories where the versions are hosted. In the case of Android, you'll probably be getting it from jcenter, for which you can find the repository page, which has all the available versions listed.

You can also browse the raw maven repository of jcenter where the files are actually hosted by going here, or look up Kotlin either on mvnrepository or on mavencentral (raw version of the latter here).