Haven’t used all the data. Can I carry over?

[dalyer]

If you're on the €12.99 plan then this is irrelevant because it comes with unlimited domestic data.

• https://48.ie/memberships

The only way to carry data over from one monthly plan to another is via the Flexi Data Safe:

• https://community.48.ie/t5/The-Knowledge-Base/Flexi-Data/ta-p/53114

Otherwise a plan's unused data and other allowances expire when the monthly plan expires. 

If you need to contact 48 support about this then see the links in my signature below.