Sorry guys, but neither updating nor any other recommendations help. There is the following bug with the shipping costs (Flat Rate):
a) leaving the "cost per order" empty, DEACTIVATES the shipping method, even that the flag is set to ENABLE. That is obviously a bug.
b) any amount as "cost per order" enables the shipping method, but also sets the shipping cost total. This means, the additional costs (e. g. 3% handling fee) will not be considered at all. That is another bug.
c) adding any amount as "Cost" at additional costs, deliveres a completely wrong result (see below):
99 price for product, including 7% VAT
1 Cost per order (non taxable)
1 Cost at Additional Costs
3% as Handling fee at Additional Costs
delivers a flat rate of 4,78.
My expectation is to get 99x 3% = 2.97