If you mean making a UK call from Ireland then you need an active membership and also cash credit on your account to pay for international calls:
Calls to Northern Ireland landlines dialled with the 048 rather than 00 44 prefix are covered by membership plan national call minutes.
For roaming issues the usual advice applies:
Unfortunately many people still seem to have problems with roaming abroad on 48 for some reason.
If your SIM predates January 2023 then a replacement may mitigate or eliminate roaming problems:
It may be worthwhile reviewing these two threads in case any of the suggestions help to avoid roaming problems:
If you have returned to Ireland from roaming abroad and are having problems using the 48 network/calls/texts/mobile data then see this key post, in particular the section titled "Returned Home?":
If you still have problems then you'll probably need to contact 48 support for further assistance.
