Cannot apply snapshot plugin for OpenAPI

I am trying to get a SNAPSHOT of a plugin that may fix our issue, but the I cannot get the library:

plugins {
    kotlin("jvm") version "1.7.10"
    id("maven-publish")
    id("org.jetbrains.kotlin.plugin.serialization") version "1.7.10"
    id("org.openapi.generator") version "6.1.0-SNAPSHOT"
}

I have already added all the necessary repositories, but still get this error: Plugin [id: 'org.openapi.generator', version: '6.1.0-SNAPSHOT'] was not found in any of the following sources (If I use the released 6.0.1 version, everything works fine)

Attempt 2: I have tried to get the plugin in another way.

buildscript {
    repositories {
        maven("https://companyserver.io/company-maven-snapshot")
        // or, via Gradle Plugin Portal:
        // url
    }
    dependencies {
        classpath ("org.openapitools:openapi-generator-gradle-plugin:6.0.1")
    }
}

apply(plugin="org.openapi.generator")

This seems to find the plugin, but I still get an error on the first line of:

openApiGenerate {
    generatorName.set("kotlin")
    inputSpec.set("$projectDir/mapi-open-api-spec.json")
    modelPackage.set("mapi.generated.models")
    apiPackage.set("mapi.generated.apis")
    invokerPackage.set("mapi.generated.invokers")
    configOptions.put("library", "multiplatform")
    typeMappings.put("kotlin.Any", "kotlin.String") // change autogenerated data type of generated templates
    kotlin.sourceSets["main"].kotlin.srcDir("$buildDir/generate-resources/main/src/main/kotlin")
}

The error: .../build.gradle.kts:75:1: Unresolved reference: openApiGenerate

I am a bit stuck now, any ideas?