warning: Kotlin runtime JAR files in the classpath should have the same version

It seems that your project is configured in such a way that you depend on kotlin-stdlib 1.1 and kotlin-reflect 1.0. The most likely case is that you already have an explicit dependency on kotlin-stdlib 1.1 but have no dependency on kotlin-reflect, and some other library (which you depend on) depends on kotlin-reflect 1.0.

If that indeed is the case, the solution is to provide an explicit dependency on kotlin-reflect 1.1.

In Maven, add this to pom.xml:

    <dependencies>
        <dependency>
            <groupId>org.jetbrains.kotlin</groupId>
            <artifactId>kotlin-reflect</artifactId>
            <version>1.1.0</version>
        </dependency>
    </dependencies>

In Gradle, add this to build.gradle:

dependencies {
    implementation "org.jetbrains.kotlin:kotlin-reflect:1.1.0"
}

See some info about this and related warnings in the official docs.

firstly, figure out the reason by the gradle script below

./gradlew app:dependencies

(change app to your gradle module name)

+--- project :common
|    +--- org.jetbrains.kotlin:kotlin-stdlib:1.3.61
|    |    +--- org.jetbrains.kotlin:kotlin-stdlib-common:1.3.61
|    |    \--- org.jetbrains:annotations:13.0
|    +--- org.jetbrains.kotlinx:kotlinx-coroutines-core-common:1.3.3
|    |    \--- org.jetbrains.kotlin:kotlin-stdlib-common:1.3.61
|    +--- org.jetbrains.kotlinx:kotlinx-serialization-runtime-common:0.12.0 -> 0.14.0
|    |    \--- org.jetbrains.kotlin:kotlin-stdlib-common:1.3.60 -> 1.3.61

Then, the dependency tree will be shown. check which dependency use the issue dependency.

If you found the dependency, decide how to solve it.

1. upgrade the dependency's version(the dependency's latest version may refer to latest issue dependency's version)
2. or exclude the issue dependency from the dependency
3. or follow other answers.

I'm not sure what is the best way. kindly just refer to it.