If you click on the customers section in 365 and go to invoices. You have the option to either add invoices one at a time by clicking “+ Invoice”, or you can upload 50 invoices at a time from your computer by clicking “Upload invoices”.
The end user can also use the app to upload invoices. This is done in the same way, where invoices can be added one at a time, or up to 50 from their gallery.