If you need to request more information regarding an invoice you can follow the following steps.
First of all, after logging in on Yakkyofy, you should be able to see the "Need help?" tab on the botton left part of the dashboard:
Once clicked on there, you should please select "Contact us":
You will land on this page, where on the right part you will see the "FAQ Center", while on the left you will see the "Category" tab:
By clicking on "Category", you will then display a menu on which you will find the option "Invoice":
Once "Invoice" gets selected, you will see the following page:
On the right, please fill in the "Problem Description" section and add the invoice number. Moreover, you can also add a screenshot of the error you are encountering as an attachment. Eventually, please click on "Send".