Hey
Just wanted to double check, but were you looking to create a tax or a surcharge for the invoices? If you created an amount as a tax, it should show up as long as you have selected the items that you want to have taxed. To do so go to Items>Sales Tax> Then choose Apply to Items next to that tax.
If you were looking to add a surcharge, (which I see is now available to be added to invoices) you can create one by going to Accounts & Settings > Business > Services Charges.
Once you create the invoice you will have the option to add the service charge if desired as well as the tax should show up assuming the tax was applied to the items on the invoice.
Let me know if that helped.
Cheers
