Message about charges despite being in EU

My partner's on a cruise round Norway. She's got roaming set up correctly on her iPhone (and is nowhere near her 12Gb EU data limit), but received a Smarty message saying "Oops. It looks like this service isn't covered in your plan, To find out how to use this service, go to https://go.smarty.uk when you have WiFi", and a list of charges, and "You need a Cash Add-on" etc. Why might she be getting this?