Just used firebase into project and getting this error : Plugin [id: 'com.google.gms.google-services'] was not found in any of the following sources

Question

When I'm running my flutter apk in android it is giving me this error.

* What went wrong:
Plugin [id: 'com.google.gms.google-services'] was not found in any of the following sources:

- Gradle Core Plugins (plugin is not in 'org.gradle' namespace)
- Included Builds (None of the included builds contain this plugin)
- Plugin Repositories (plugin dependency must include a version number for this source)

* Try:
> Run with --stacktrace option to get the stack trace.
> Run with --info or --debug option to get more log output.
> Run with --scan to get full insights.

* Get more help at https://help.gradle.org

BUILD FAILED in 2s
Error: Gradle task assembleDebug failed with exit code 1

This is my how my build.gradle file looks like -

plugins {
    id 'com.google.gms.google-services'
}


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

rootProject.buildDir = '../build'
subprojects {
    project.buildDir = "${rootProject.buildDir}/${project.name}"
}
subprojects {
    project.evaluationDependsOn(':app')
}

tasks.register("clean", Delete) {
    delete rootProject.buildDir
}

dependancies {
    classpath 'com.google.gms:google-services:4.4.1'
}

Please help me... need to submit the project really soon.