Hello ! I want to be able to take a certains invoice and make a new estimate with the same custom items in it and prices and implement that in a workflow

my problem is that I can't seem to get that data from GET invoice request where I can get everything like the customer name, total price, billing adress, etc. I was wondering if there was any way to just basically get the content of an invoice like that ? I guess Ill need a do a custom script but I dont even have the info I want inside the GET resquest for the invoice ?