Hi Tom,
The main reason we don't show the detail there is because it supports paying the invoice without the user being authenticated therefore any user could view what is shown and that could leak information that we don't want to be public.
I've added a to do item in our project tracker so that we can show more detail in the case where the user is authenticated and we know the invoice belongs to that user.
I've also added a to do item to create a setting to allow you to edit some html to be shown on the page so you could add some general informaiton or instructions that everyone would see.
Best,
Joe