Hi there, @Pete650.

Thanks for sharing the steps that you've take to resolve issue.

Let's try opening your account on another supported browsers. This might be a temporary issue with your current browser and QuickBooks. That way, you can save your customization. 

The following browsers are supported on both web and mobile devices:

• Google Chrome: version 78 or newer
• Mozilla Firefox: version 76 or newer. Note: To preview and print forms on Mac OS, you'll also need the Firefox PDF plugin.
• Microsoft Edge: version 75 or newer
• Safari: version 12 or newer (Mac only)
• Opera: version 68 or newer
• Samsung: version 10 or newer

To know what computer and browser you need for the best experience when using QuickBooks, please check out this article: System requirements for QuickBooks Online.

I've also included a detailed resource about customizing sales forms and creating recurring templates in QuickBooks: 

• Customize invoices, estimates, & sales receipts
• Create recurring transactions in QuickBooks Online

Let me know if you need further assistance with the customization process. I’ll get back to help and make sure this is taken care of for you. Have a great rest of the day.