Hi there, jazzolina.
Thank you for visiting the QuickBooks Community. I'll be sharing troubleshooting steps to ensure you can use the Custom number feature to manually change/enter invoice numbers. Beforehand, may I ask if you received an error or if the box for Custom transaction numbers is grayed out? I also appreciate adding a screenshot on your end so I can present an accurate solution.
For now, I recommend logging in to your QuickBooks account using a private browser. Then, try to utilize the custom function and change the invoice number from there. This is to rule out the possibility of a webpage issue, and private browsing doesn't store local files or cache.
Use these keyboard shortcuts based on the browser you're using:
- For Firefox or Microsoft Edge, press Ctrl + Shift + P.
- For Chrome, press Ctrl + Shift + N.
- For Safari, hold down Command + Shift + N.
If it works in incognito, you have to clear the cache of your regular browser. This removes the history or log of sites so you can start with a clean slate. You can check this article to see the steps: Clear cache and cookies to fix issues when using QuickBooks Online.
If the steps above didn't work, use another supported browser as an alternative.
Lastly, you may refer to this article to see details on how the Sales page provides you a great at-a-glance view of the status of sales transactions like open and paid invoices: View sales transactions.
Let me know if there's anything else you need help with managing your invoices. I'm always here to help you anytime. Take care and keep safe!