Hello there, Angel. 

Generally, you can set up the terms of your invoice in QuickBooks Desktop. May I know what specific issue you encountered when you said you were having trouble getting the due date of your email when sending invoices? This way, we'll be able to properly assist with your concern. 

A screenshot would also be very much appreciated so we'll be able to determine what causes the issue. Anyway, if you have any questions concerning invoices, or when emailing your customers paid invoice, let us know so we can get back to you as soon as possible.