Hi there,
I have had the same issue in France, ever since VAT is prepaid, although the extra costs seem to be much lower here (around 10 €). I had earlier asked for IOSS and transaction numbers to be printed on the posting label. I now wonder if the issue is not that USPS add their own label on top of Paizo's. This maskes the VAT as USPS only prints the VAT included price with no particular precision.
No issue with Legendary Games shipments here (I received print items for the Boricubos kickstarter with no similar issue).
