Hi there, info992.
There are times that the browser is holding too much data, which can cause unusual behavior in QuickBooks Online.
I suggest logging in your QuickBooks account using a private browser. This way, you'll see if you get the same result. And, to check if the full cache is causing the problem. This might be also the reason that the next invoice still T-036-21 even your last invoiced was changed to T-20-036.
Use these keyboard shortcuts based on the browser you're using.
- For Internet Explorer of Firefox, press Ctrl + Shift + P.
- For Chrome, press Ctrl + Shift + N.
- For Safari, hold down Command + Shift + N.
If it works in incognito, I recommend clearing the cache of your regular browser. This way, it can resolve many different issues and is a good place to start whenever you see unexpected behavior in the product.
If the steps above didn't work, use another supported browser as alternatives.
Please check this article on how to personalize your sales forms and to add additional information to enhance your business' brand: Customise invoices, estimates, and sales receipts in QuickBooks Online.
Please know that you're always welcome to post if you have any other concerns. Wishing you and your business continued success.
