Google Play App Signing - KeyHash Mismatch

I had the same issue and it appears that as you say, the Google Play Store re-signs your apk with a new key, and this what you must provide to Facebook as the key hash (not the one generated using keytool).

The second half of this answer https://stackoverflow.com/a/44448437/2640599 is useful.

Basically you need to provide Facebook with the hash based on the SHA-1 App signing certificate Google generated, instead of using keytool and your local key (which it seems is now just used for uploading to Google).

You have to use the SHA-1 key generated by Google. Following steps would fix it.

1). Go to Google console => your project => Setup => App Integrity => App signing key certificate.

2). Copy SHA-1 certificate from there and as it's in hexadecimal and since Facebook needs it in base64 so use the command shown in step 3

3).echo SHA-1 key from step-2 (Hexadecimal) | xxd -r -p | openssl base64
This command won't work in command prompt use bash on windows or git cli.

4). Paste the base64 key in Facebook console => Settings => basic => key hashes

Most of the answers above are correct but instead of running hash command there is a great tool for that, so i will re-state the steps using @neeraj's answer as the base answer:

Step 3 is the only changed item

You have to use the SHA-1 key generated by Google. Following steps would fix it.

1). Go to Google console => Release Management => App signing => App signing certificate.

2). Copy SHA-1 certificate from there and as it's in hexadecimal and since Facebook needs it in base64 so use the online tool shown in step 3

3). go to https://base64.guru/converter/encode/hex to convert hexadecimal to base64

4). Paste the base64 key in Facebook console => Settings => basic => key hashes

You can convert SHA-1 hash in hex format (as found in Play console) into base64 hash using next command (on maybe Git Bash):

echo 33:4E:48:84:19:50:3A:1F:63:A6:0F:F6:A1:C2:31:E5:01:38:55:2E | xxd -r -p | openssl base64

Output:

M05IhBlQOh9jpg/2ocIx5QE4VS4=

This hash can be used for example when setting up Facebook app. Answer Source