Post All Invoices Shows Prompt for Zero GST or GST Exempt Invoices

I am trying to post my invoices from the Manage Invoices screen.  I cannot select Post or Post all, without getting a prompt for some of them.  The reason says "Invoice has no GST".  

Solution

Invoices that do not contain GST have to be opened and processed from inside the Invoice itself, to ensure that the user is aware that the Invoice contains no GST.  

If a Customer does not incur GST, they should be set to International Customer (GST Exempt) to prevent this prompt from appearing.

"GST is zero on this Invoice. is this correct" will appear. If this is correct, select Yes and the invoice will process as usual.

If the Invoice should have GST and it does not, select No and a second message will appear.