How can I remove a custom field from my invoice template after downgrading to a version that doesn't support custom fields.

It's nice to see you here in the Community space, md-holmpc.

I know how to achieve your goal while managing your invoice templates in QuickBooks Online. Let me guide you through the detailed process.

Regarding this issue, we can delete and create a new invoice template to remove those custom fields when downgrading. But before doing so, ensure to take note of the details so you can seamlessly modify the template once you recreate it.

When you're ready to delete the template, here's how you can do it:

1. Choose Custom form styles from the Gear icon.
2. Find the invoice template.
3. Click the dropdown icon under the Action column.
4. Select Delete and tick Yes, delete this style to confirm.

Once done, you can follow this guide make a new template, and personalise it according to your needs: Customise invoices, estimates, and sales receipts in QuickBooks Online.

If you'd like to track your invoices in the future, here's an article you can use to pull up some reports available: Run reports in QuickBooks Online.

Feel free to reply on this thread if you have further questions about the information above. I'd be here to answer it for you. Have a nice day.