Support
The quickest way to reach me is email. Write to support@iamjarl.com and tell me what you were trying to do and what happened. It helps a lot to include the app version, which is under It's mono, yo! in the menu bar, then About, and your macOS version.
Ask in public
If you would rather ask where other people can see the answer, the app has had a thread on Elektronauts since March. I follow it, and so do people who use the app with their own samplers.
Bugs and the source code
It's mono, yo! is open source. If you have found a bug and you are comfortable with GitHub, you can also open an issue there. Two of the fixes in the 1.4 releases started exactly that way.
What reaches me
Only what you send. The app itself sends nothing anywhere, so it cannot tell me when something goes wrong, and I would much rather hear it from you directly than find it in a review. The privacy policy has the details.