Currently, the amount that is being added is 4% + 72p (even though it is supposed to be 75p).
No idea why it is 72p and not 75p - but that is why the figures are not right when you try to calculate them or set your prices to take account of the fee.
"There are two ways to be fooled. One is to believe what isn't true; the other is to refuse to believe what is true.”
Søren Kierkegaard, Danish philosopher (1813 - 1855)