Found the line in strings of jelly.elf
```
echo "bitcoin: G9mzcaHrPAZnkfMCgsNrt5Y8VXSfV74E2kNhYeaWgPYCrtNDzZzC" > flag.txt
```

We know Bitcoin addresses are written base58 and start with 0x80

Decoded the hash

```console
➜ jelly echo G9mzcaHrPAZnkfMCgsNrt5Y8VXSfV74E2kNhYeaWgPYCrtNDzZzC | base58 -d
flag{a70f5c001e67e4c26bf20dc457d43459}
```

Original writeup (https://github.com/giorgosioak/ctf-writeups/tree/main/NahamCon/2022/Jelly).