Welcome to the Community, @ibrahim2.
Let's perform some troubleshooting steps so you can customize an invoice template successfully.
Before we start, did you encounter any error message when accessing the Custom Form Styles page? Any additional information would be greatly appreciated.
There are times that the browser stores frequently-accessed data, thus causing websites, like QuickBooks Online (QBO), to act weirdly. Let's try logging to your QBO account using a private browser.
To use a private browser, here's how:
- Google Chrome: Ctrl + Shift + N
- Internet Explorer: Ctrl + Shift + N
- Mozilla Firefox: Ctrl + Shift + N
- Safari: Command + Option + N
Once logged in, go back and try to customize an invoice template again to double-check.
If this works, it means that you need to clear your browser's cache so the system can start fresh.
If you get the same result while using a private browser, I'd suggest using a different one.
Just in case you want to import custom form styles, feel free to check out this article for the detailed steps and information: Import custom form styles for invoices or estimates.
Please keep in touch if there's anything else I can do to help you succeed with QuickBooks. I've got your back. Have a great day.