The VAT late payment penalty is separate from the late filing penalty — filing on time does not protect you from a payment penalty if the money reaches HMRC late.
Most overseas businesses register using the standard online service or the VAT1 form. A separate form, the VAT1TR, is needed where a UK tax representative is being appointed.
As an overseas seller on Amazon, HMRC classifies you as an NETP from your very first sale, regardless of how small or new your business is.
As a non-established taxable person, your VAT return deadline is the seventh of the second month after each quarter end; filing and payment must both reach HMRC by the same date.