My custom style form dun have the function to insert an image, either signature or QR code at end of the invoice.

The ability to insert an image, such as a signature or QR code, on your invoice is a new feature that is currently being rolled out to accounts. It's possible that your account hasn't received this feature yet.

However, if you can see this option on some form styles but not others, try deleting and recreating the affected custom form style to reflect the new feature.

Let us know if you have any other questions. We're happy to help!