I managed to generate a signed bundle by following this suggestion. I edited the google-services.json client’s package name to match the name in File/ProjectStructure/BuildVariants/ApplicationIDSuffix .
"client": [
{
"client_info": {
"mobilesdk_app_id": "intentionallyLeftBlank",
"android_client_info": {
"package_name": "com.example.aaron.myproject22"
}