I know this was from 9 months ago but I just recently had the same problem.
I was able to crack the zip password with 1234
I have no idea where the password came from, as the zipped MYOB back up file originated from MYOB online.
As for a corrupt zip file, that's just nonsense.
Make sure you use WinZip or WinRAR, as these programs throw up a password dialogue box upon initialising the extraction.
The built-in zip extractor in Windows 11 just won't extract and doesn't offer a password dialogue box.
A 50 minute wait for a 5 minute talk to MYOB tech support revealed nothing. "We don't insert passwords when zipping files for you to download". "You must've put the password in it"
Anyway, after about 8-10 days of churning with Kraken v1.5 I had a password!!!
Such a relief, with no help from anyone.
So rquad3, if you are still locked out try 1234.