when adding new invoice,
1. whether possible , after selecting customer, to show the country on the invoice screen?
2.entering customer, possible by customer code? if yes, do i use a custom field as customer code. Then how to adjust the invoice screen to select by customer code?
i dont think i understand your first question
if i understand your seconds question right, simple invoices has no way of doing that, you could assign codes and have them appear on invoices using customer fields but you couldn't select a customer by code, you would need some make some significant changes to simple invoices to allow this