The currency you'll be charged depends on the address of the billing entity you have set up, which, in turn, normally depends on the country/ies where your covered employees are based.

If you have a billing entity with an address in the UK linked to your benefits, you'll be charged in GBP. On the other hand, if your billing entity is based in Ireland, you'll be charged in EUR.

Should you have multiple billing entities in different countries, you'll be charged in EUR for Irish benefits and, separately, in GBP, for the UK benefits.