This is the VAT you pay to the UK authorities. However, this does not come from your pocket. Global-e pays you an additional 20% on the order and Global-e then can claim it back from the authorities.

Example:

Item on your site is 100 GBP

Global-e pays you 120 GBP ( 100 GBP + 20% VAT)

You pay the authorities 20 GBP

This way you pocket the original price

How it looks in the reconciliation report: