When I'm editing an invoice, it doesn't want to save. It gives an error message which means I can't send the invoice.

Let me help you resolve this error and save your invoice successfully, @superglasswp-gma.

We can isolate this issue by performing some steps. Here's how:

1. Open your QuickBooks Online account in a private browser or incognito. This mode prevents your browsing history from being stored.
   Ctrl + Shift + N for Google Chrome
   Ctrl + Shift + P for Mozilla Firefox and Microsoft Edge
   Command + Shift + N for Safari
    
2. Open the existing invoice and save it. If it works, you can go back to your regular browser and clear its cache.
3. Restart your browser to refresh the settings.
4. Try using a different supported browser as another option.
    

You'll want to personalize sales forms in QuickBooks Online. Feel free to check this article for the details: 

• Customise invoices, quotes, and sales receipts.
• Add, customise, or remove logos on sales forms.

You can also share the exact error message you received. 

Please keep me updated on the result. I want to make sure this is resolved for you. Stay safe, superglasswp-gma!