For goods valued above €150 then the import VAT has to be paid in the country of destination. If the business is registered for IOSS in one of the EU countries then it would be worth checking with their tax office on how to register sales over the limit.
It also depends on how the company is set up and where the goods are warehoused. If they are stored in an EU country then an EU-EU B2C sale can be made once the goods are imported into that country (and some operate postponed import VAT in a similar way to the UK). If they are stored in GB (not Northern Ireland) then the import VAT must be charged and paid for by either the customer or the exporter, possibly via the freight forwarder.
Hope this helps.