This topic explains the particularities of tax setting for UK-based online shops using only IOSS special VAT scheme and selling predominantly to the UK, to EU, and other countries (USA, Asia, etc.)
We generally propose that such UK IOSS customers use an inclusive pricing model for their WooCommerce shops.
With normal settings for the UK tax zone:
This model means that prices in the catalog are kept with VAT in the catalog. Price in the shop display with the properly set geolocation will render VAT-inclusive prices for UK and VAT-exclusive prices for the EU.
Setting on the EAS side is made VAT exclusive since the WC engine will remove UK VAT from the catalog price before putting it into the cart.
Further calculations are done as if the price was exclusive, i.e. consumption country VAT will be added to the merchandise cost.