Hi, me iz Basement Cat!
Here iz flag: 5jsnZDgv9EfFeoGXZrFurdz7MWAnK2WaPfszFadr
The bolded word “Base” in the challenge description was a clear hint that the flag has been encoded with a binary-to-text encoding scheme (i.e. Base-X).
Pasting the string into CyberChef auto-detects it as Base58:
The accepted flag was,