SHA Stands for the Secure Hash Algorithm, which used to identify your android app instead of a Client ID. You can generate it from your Android studio or External Software or From Play Console.
When Your App is Live then You should get the SHA1 Key from your Play Console Dashboard. SHA1 Key is different for all of your Apps which is available on the Play Console.
SHA1 Key used when you have integrated the Firebase or Social login features in your Android App.
How to Generate or Get SHA1 Key on Google Play Console:
First of all Login to your account then go to All Apps > then choose your app which you want to get the SHA1 key For Firebase.
Then go to Setup Menu > App Integrity > You will see: as shown in the below screenshot:
App signing key certificate and Upload key certificate
Copy Both Both SHA1 Key From App Signing and Upload key then paste these both SHA1 Key on your firebase console app.
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