Let's add a signature section to your invoices, mrsedaghati.

You can add Received by: on the Message on invoice box, so it will be printed on the invoice and your customer can sign the invoice.

You can also add the message to your invoice template, it will automatically come our every time you create invoices.

1. On an Invoice page, click Customize at the bottom.
2. Select Edit current to customized the checked template.
3. Click the Content bar and click the lowest section of the previewed invoice on the right side.
4. Enter Received by: in the message box. Refer to the screenshot.

If there are other things that you need to show on your invoices, please let me know.