I have an application based on models but I don't create it, I need to convert the value of an invoice into numbers, who guides me. This is the form, I want the field marked in yellow to appear in letter in the black box.

I have an application based on models but I don't create it, I need to convert the value of an invoice into numbers, who guides me. This is the form, I want the field marked in yellow to appear in letter in the black box.