Why is there an "a" being added to invoice numbers all of the sudden?

Hello robbie2, 

Welcome  to the Community. It's essential you're able to use the program without running into issues. Don't worry, I've got your back. I'll be happy to steer you in the right direction so you can get back to doing what you enjoy. 

I'd like to start off by troubleshooting this issue to determine if it's a browser-related issue. Clearing cache and cookies is a great way to clean your browser allowing it to work more efficiently. Here's an article that shows you how to do that: How to clear cache and cookies. If this doesn't work, I suggest using a private/incognito window to see if that works instead. Try this out and let me know what happens. In case this issue persists, I encourage you to contact our support team so they can assist you further with this. Here are our contact details: 

• Schedule a Callback or start a Chat: click (?) in the upper right in QuickBooks Online > enter "Contact support" > choose Contact Us > provide a brief summary > select Let's Talk > choose Get a callback or Start a Chat.
• Social Media: Facebook, Twitter, and Instagram.
• Support hours are from Monday to Friday between 9 a.m. and 8 p.m. ET.

I'll be one message away in case you need further assistance.