I need to add an invoice amount and invoice number to my template payment form.

You can add an autoresponder email to your Order form and edit the email template by following this guide: https://www.jotform.com/help/430-How-to-Edit-the-Email-Template-for-Notifications-and-Autoresponders

Another related guide that can help you on creating an Invoice email alert: https://www.jotform.com/help/231-How-to-Strip-Payment-Labels-and-Separate-Payment-Info-on-Email-Alerts

Try it and if you have questions, please let us know. Thank you.