Plugin with id 'com.guardsquare.proguard' not found

I followed the instructions in github.
I have just a scala project, no android.
At the start of the build.gradle file, I have

buildscript {
    repositories {
        mavenCentral() // For the ProGuard Gradle Plugin and anything else.
    }
    dependencies {
        classpath 'com.guardsquare:proguard-gradle:7.1.1'  // The ProGuard Gradle plugin.
    }
}

Then have

apply plugin: 'com.guardsquare.proguard'

but when I try to build
I get

A problem occurred evaluating script.
> Plugin with id 'com.guardsquare.proguard' not found.

I am using gradle 7.3-RC5

Hi @Barry_Becker,

Thanks for presenting this to us. We would advise not applying the plugin and to follow the directions on our manual page here. Give that a try and let us know if it was effective.

Hope this helps!
Jesse