invokedynamic requires –min-sdk-version >= 26

It is important part:

You need to add this in that module’s build.gradle where it’s not added like app module.

android {
    compileOptions {
        sourceCompatibility JavaVersion.VERSION_1_8
        targetCompatibility JavaVersion.VERSION_1_8
    }
}

Also you forgot to add repo for plugin:

buildscript {
    repositories {
        jcenter()
        google()
    }
}