I would suggest rather using the entry point CALPIEDHT in source file TRTVENFACC. You can find more information about the entry point in the help file, link attached below:

online-help.sageerpx3.com/.../

Thank you, Regard. I read that the entry point CALPIEDHT in source file TRTVENFACC is directed towards the sales invoice, but my issue is with getting the calculation on the sales order before moving to the actual invoice. We are wanting the processing fee to include other invoicing elements for customers that need to prepay on an order.

The screen SIHV is a global calculation screen that is used on all sales transactions. You can use the GABREV variable to test the current function, but the invoicing element calculation is all done on this screen and can be edited using this entry point. If you wish to use the definition on the actual invoicing element, the action as indicated above, then using the screen shot below, you source file XXCALC would contain the following:

$ACTION
Case ACTION
When "CALC" : Gosub CALC
When Default
Endcase

Return

$CALC
# VARIABLE WMNTCLCBAS IS SET TO THE BASE AMOUNT TO WHICH THE CALCULATION WILL BE APPLIED
If dim(WMNTCLCBAS)>0
WMNTCLCBAS = XXX
Endif

Return