Total amount is not showing in header

I created my own invoice template but when I try to display the total amount in the header the total does not display. All other fields in header show eg date and invoice number. The total amount does show in the body its just the header. Please see image attached of my issue.

Where have you added the total amount from?

It should be either $aos_invoices_total_amt or $aos_invoices_total_amount