I just got a sale (32€) to United Kingdom, but the UK VAT tax has not been collected and doesn't appear in invoice, however VAT processing fee 0.37 has been charged from my payment account.
VAT processing fee is the VAT you pay on the processing fee you've been charged by Etsy.
It's VAT on seller services.
If VAT has not been charged to your customer at the time of purchase, he will be liable for it at the time of delivery plus a handling fee charged by Royal Mail (£8). Either you inform him before sending the order or you cancel the order and ask him to place a new order (assuming that it is a temporary bug). Hope this helps !
If there is VAT to be paid then it will be charged by the Royal Mail on collection of the mail from the collecting office. This makes no difference to the seller. Ordering again will not make any difference as VAT will then need to be charged by the Royal Mail on that order.
Of course, VAT charged by the Royal Mail makes no difference for the seller. But it makes a difference for the buyer : the £8 handling fee. Hence my proposal of cancelling the order and placing a new one in case the non-collection of VAT was a temporary glitch.