How to record expenses where GST invoice is issued later?

How to record expenses where GST invoice is issued later?

Hi there

We have many expenses (flights, hotels, stationery etc) for which the supplier issues a proforma invoice and then supplies a tax invoice a few days later. The proforma invoices generally don't have any GST information on them.

Currently, we are manually maintaining a list of pending invoices and manually adding the GST invoices when we receive them. Obviously, this leave a lot of room for mistakes. 

What is the best way to handle this? 

Cheers!