Glad to have you here in the Community, @nick47.
You can simply click the X icon of the attached file to remove it from the invoice. Let me walk you through the steps.
- Find and open the invoice transaction.
- Scroll down a bit until you've reached the Attachments section.
- Click the X icon to remove the attachment.
- Hit Save and close.
Here's an article you can read for more details: Attachments in QuickBooks Online.
As always, feel free to visit our QuickBooks Community help website for QuickBooks Online if you need tips and related articles in the future.
Please know you can continue to reach me here with any additional questions. Thanks for coming to the Community, wishing you continued success.