There are 5 main issues with the IOSS PDDP that I can see:

1) The duty for the US suddenly increased on my items from 10% to 25% without warning or even anything on the Royal Mail updates to say the duty had increased. We didn't know until we shipped something out!

2) Why do Royal Mail charge a £1 handling fee even if the recipient is to pay the duty and taxes at their end?

3) The EU duty (at least) is calculated wrongly. Tried sending an item to Denmark worth £13 - except that when adding to the order, I increased the quantity to 2.

With "Taxes have been prepaid via IOSS. I will pay and duties & fees" set, the estimated EU duty was £12.04 !!

On the Apply Postage page, reduce the quantity to 1 and the estimated EU duty is £3.56. Increase the quantity back to 2 and the estimated EU duty remains £3.56.

4) When you claim a refund for postage after generating the labels, Royal Mail pay back the postage, but NOT the prepaid duties and taxes even though they can see the item never entered their system.

5) When shipping two different items on the same order - Royal Mail collect a handling charge for EACH item - which seems wrong - it should be one handling charge for each order

Raising a support ticket for comments on (1) and (4) gets no response at all.