The €7.99 plan is no longer available to new customers.
Only the €12.99 plan.
If you want to join 48 get a free SIM here:
Or, better still, get an existing 48 customer to give you a referral link and you both get rewards:
To port your number from another provider to 48 see here:
When I try to transfer from EIR it says "Must be an Irish mobile number", why?
Are you definitely entering your number in 10 digit 08xxxxxxxx format? If so, and it's generating that error message, then you'll need to contact 48 support. See the link in my signature below or email them at firstname.lastname@example.org