当未定义auth密钥字符串(通常称为Api密钥)时，会发生此错误.因此，请检查google-services.json文件并将您的密钥放在current_key标记中.然后重建项目，以便该应用程序使用api密钥.

This error occurs when the auth key string , commonly known as Api key, is not defined. So check the google-services.json file and put your key in current_key tag.And rebuild the project so that the app uses the api key.