Flutter Run Error "Could not resolve androidx.window:window:[1.0.0-beta04]"

I have picked up an old flutter application from another developer and I am having difficulty getting it to build. When I try 'flutter run' I get the following error:

FAILURE: Build failed with an exception.

* What went wrong:
Could not determine the dependencies of task ':app:processDevDebugResources'.
> Could not resolve all task dependencies for configuration ':app:devDebugRuntimeClasspath'.
> Could not resolve androidx.window:window:[1.0.0-beta04].
  Required by:
     project :app > project :in_app_purchase > io.flutter:flutter_embedding_debug:1.0.0-57d3bac3dd5cb5b0e464ab70e7bc8a0d8cf083ab > androidx.window:window-java:1.0.0-beta04
  > Failed to list versions for androidx.window:window.
     > Unable to load Maven meta-data from https://google.bintray.com/exoplayer/androidx/window/window/maven-metadata.xml.
        > Could not get resource 'https://google.bintray.com/exoplayer/androidx/window/window/maven-metadata.xml'.
           > Could not GET 'https://google.bintray.com/exoplayer/androidx/window/window/maven-metadata.xml'. Received status code 502 from server: Bad Gateway

* 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 6m 38s

Has anyone come across this before? Do you know what causes it and/or how to rectify the issue?

I am very new to flutter, so please let me know what further information is requried to diagnose this issue.

FYI, I have removed jcenter() from repositories, but it doesn't seem to help. Here is build.gradle:

buildscript {
    ext.kotlin_version = '1.3.50'
    repositories {
        google()
        mavenCentral()
        // mp035 removed
        // jcenter()
    }

    dependencies {
        classpath 'com.android.tools.build:gradle:3.5.4'
        classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"
        classpath 'com.google.gms:google-services:4.3.4'
        classpath 'com.google.firebase:firebase-crashlytics-gradle:2.6.1'
    }
}

allprojects {
    repositories {
        google()
        mavenCentral()
        /// mp035 removed
        //jcenter()
    }
}
ext.flutterFFmpegPackage = 'full'

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

task clean(type: Delete) {
    delete rootProject.buildDir
}