You can either add maven { url 'https://jitpack.io' } directly to the build.gradle file of the project or include it to the plugin using the following approach:

[rootProject, this].each {
    it.allprojects {
        repositories {
            maven { url 'https://jitpack.io' }
        }
    }
}

This setup will look like:

allprojects {
    repositories {
        google()
        mavenCentral()
    }
}

[rootProject, this].each {
    it.allprojects {
        repositories {
            maven { url 'https://jitpack.io' }
        }
    }
}

apply plugin: "com.android.library"
apply plugin: "kotlin-android"

ref: 1 2