In Thailand, I need to get a manual signature from the delivery driver and the customer. I can't find where to add this signature lines in the invoice

Welcome to the Community, userbill.long.

Right now, adding a signature line to the invoice is not an option. As a workaround, you can use the Message on invoice field from to include the information you need. 

I know the benefits of having this option would be helpful in the system. Your input and insights about the products’ features will guide us on how to make the program works best for your business. 

While we continue to make your experience with us even better, I recommend visiting our QuickBooks Blog to get the recent news, information about the latest features, and updates. 

If you need further assistance in managing your account, leave me a comment below. It's always a pleasure to help you. Take care.