Could not create domain object 'gpr' (MavenPublication) in build.gradle.kts

Question

Hey I am trying to publish kmm library in github packages. I followed this doc. But I don't understand

1. what is project.findProperty("gpr.user") and ("gpr.key")?

2. I used macos so System.getenv("USERNAME") and System.getenv("TOKEN") is relevant ?

build.gradle.kts

plugins {
    kotlin("multiplatform") version "1.6.21"
    id("com.android.library")
    id("maven-publish")
}

group = "com.abc"
version = "0.0.1"

repositories {
    google()
    mavenCentral()
}

kotlin {
    android {
        publishLibraryVariants("release", "debug")
    }
    android()
    iosX64()
    iosArm64()
    iosSimulatorArm64()

    sourceSets {
        val ktorVersion = "2.0.0"
        val commonMain by getting 
        val androidMain by getting {
            val iosX64Main by getting
            val iosArm64Main by getting
            val iosSimulatorArm64Main by getting
            val iosMain by creating {
                dependsOn(commonMain)
                iosX64Main.dependsOn(this)
                iosArm64Main.dependsOn(this)
                iosSimulatorArm64Main.dependsOn(this)
            }
        }
    }
}

android {
    compileSdk = 21
    sourceSets["main"].manifest.srcFile("src/androidMain/AndroidManifest.xml")
    defaultConfig {
        minSdk = 21
        targetSdk = 31
    }
    @Suppress("UnstableApiUsage") compileOptions {
        sourceCompatibility = JavaVersion.VERSION_1_8
        targetCompatibility = JavaVersion.VERSION_1_8
    }
}

publishing {
    repositories {
        maven {
            name = "GitHubPackages"
            url = uri("https://maven.pkg.github.com/OWNER/REPOSITORY")
            credentials {
                username = project.findProperty("gpr.user") as String? ?: System.getenv("USERNAME")
                password = project.findProperty("gpr.key") as String? ?: System.getenv("TOKEN")
            }
        }
    }
    publications {
        register<MavenPublication>("gpr") {
            from(components["java"])
        }
    }
}

Error

Build file '/Users/vmodi/IdeaProjects/abc/build.gradle.kts' line: 88

Could not create domain object 'gpr' (MavenPublication)
> SoftwareComponentInternal with name 'java' not found.