What's your script trigger?  PreTotals?  If so, there is no oHeaderObj, and you can't rely on the header totals (not calculated yet).  Since you want to include SalesTaxAmt in your base formula, you'll probably have to change your script to a button on the Totals tab, instead of a PreTotals event... restructuring the script properly, with a line loop to find the fee line.

It's working now.  I had an incorrect event script running on the sales order header.  Once that was deleted, the script works great.

It's working now.  I had an incorrect event script running on the sales order header.  Once that was deleted, the script works great.

Ah... makes sense. 

Be sure to click Totals before adding the fee line.  Header totals don't get calculated until then.

You will want to make sure your script works if changes to existing lines or freight are made or new lines are added. 

Good point.  Handling back-orders is also a bit complicated.

You should also check into the legality of charging a CC fee.  Some jurisdiction prohibit such fees.

I use a UDT to qualify states so that the administrator can keep it up to date without having to change the script.