Cracking

Hi folks,
I have a cyphered phrase, H4sIAAo5tlwAA0vMyVGozC8tUkhKLE5VSCxKVUhKzcnPS1coyVcoLeYCAAH80zsfAAAA, and I know it can be decrypted because it’s a game I am playing. What are the clues that can help identify which algorithm was used? It seems it’s not base64 encoded but plain text and I have tried basic things like md5 but I cannot find out which encoding was used.
Can you please help?
Cheers