Import multiple invoices, when to use !ENDTRNS
I want to import several invoices using one IIF file. Do I need the !TRNS and !SPL and !ENDTRNS one time, or for every invoice?
I want to import several invoices using one IIF file. Do I need the !TRNS and !SPL and !ENDTRNS one time, or for every invoice?

You need to use TRNS, SPL and ENDTRNS for each transaction. The ! rows are where you define what you're importing and you can just use them once at the beginning of the import (or use them more than once but you don't need to do that.)