No biggy. I'll probably just send an SMS to keep it active. Don't think I'll be using it that much on the cruise anyway, especially since I have CBW.
Actually, the UM page right here lists a 10 euro refill as one of the options.
http://www.prepaidgsm.net/en/int/united.html
Phones: Xiaomi Mi Mix 2, Samsung Galaxy A50, ASUS zenfone 3,
Sim cards: AT&T (Contract), 3 UK, Piranha Mobile