QuickBooks Online integrates with multiple applications as long as it's supported and available from the app center. To check and verify if Onyx is supported, I encourage visiting our app center. If the app is not available from there, I encourage reaching out to our Developer Team so they can work with the connection between Onyx and QuickBooks.
Just in case you need reference while working with QuickBooks in the future, feel free to read our help articles.
Get back to me if you have any other questions. I'm a few clicks away to help. Have a good day!