You'll need to post a bit more info than that if you want help.
Are you new to 48 and just trying to get started?
If so did you activate your SIM and is your phone unlocked for use on any network?
What happens when you try to use the 48 SIM in your phone?
Or have you been here a while, it was working OK but has stopped working for some reason?
Again what are the symptoms or the issue and what error messages do you get?
What make and model of phone do you have?
As mentioned above is it unlocked for use on any network?
Please provide all of this info and anything else that may be relevant.
Help others to help you.
Hope this helps.