As ASAP has grown over the years, we have built out more features that were once useful for a few organizations and have now become functions available for all. One of the more recent changes for some organizations is the removal of the "Edit Invoice Item Fees" button found on the invoice detail page for admins. The reason for this removal is due to the addition of our "Make Adjustment" tool found towards the bottom of the invoice. Here's an article that goes into more detail as to what this button is and how it works: Editing an Invoice
As for the reasoning behind removing the original function, this was due to no longer necessitating changing single invoice items without tracking when and how much was being modified. When the original button had been used, it would change that amount on the invoice but there was no way to show when and how much was being changed from the original fee. With the new "Make Adjustment" tool, there is now tracking done on the invoice item that shows when and how much was changed.
As a note, this function has also been removed on the "User Access" page under the "Configuration" menu.