A pleasant day to you, @ROBINWHITEMGSIGLASSCOM.
QuickBooks Online lets you add negative figures and letters in the Check Number section. You can check out the screenshot below for reference:
Since this option isn't applicable on your end, it'd be best if you can provide extra details about what will prompt on your screen upon trying to enter the numbers.
For now, we can try accessing your account using a private window. This can help us isolate if the stored cache on your browser is preventing you from entering letters and negative figures in the vendor's transaction number.
You can open a Private Window in all supported browsers using the corresponding keyboard shortcut below:
- Chrome: Ctrl+Shift+N
- Internet Explorer: Ctrl+Shift+P
- Firefox: Ctrl+Shift+P
- Safari: Command+Shift+N
If it works fine, you can go back to your regular browser, and clear its cache. The cache is stored for increased loading performance, but too much can accumulate and bog down processes. I'm including an article that goes over this in more depth and provides steps for supported browsers: Delete or Disable Cache and Temporary Internet Files in Your Web Browser.
You can also check out this link about printing checks in QBO for your future reference: How to print checks.
I want to make sure you're all set, let me know if you have any other questions. Have a great day!