Before you want to build the application, you need the SHA-1 and SHA-256 for the database. This key is used for push notification of the application. You can get these keys by following this step. First, you need to change your command prompt’s/terminal’s directory to android by “cd android” command. After that, your command prompt/terminal directory will change to root/android. Then you can get the key with this command “./gradlew signingReport”.
After that, the terminal will load all the SHA-1 and SHA-256 types. Debug and Release type SHA-1 and SHA-256 are the only ones you needed for Firebase database.
After you get SHA-1 and SHA-256 signingReport, don’t forget to input it into Firebase database. So, your apps can get notifications.