getting release key hash for facebook
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For future reference, if you already have your app on Play Store you can this:
Go to Release Management
select App Signing in Release Management
You can see SHA1 key in hex format App signing certificate.
Copy the SHA1 in hex format and convert it in to base64 format, you can use this link http://tomeko.net/online_tools/hex_to_base64.php to do that without the SHA1: part of the hex.
Go to Facebook developer console and add the key(after convert to base 64) in the settings —> basic –> key hashes.