Question about the SIM card provided by Apple

I received a free 5G SIM card from Apple when I got my new iPhone 13. *I already had SIM card from old phone. The thing is I didn’t want to waste this free SIM card, so I put it into my new iPhone(like after a week after I got it). However, it isn’t working. Is it my phone’s problem or do I have to talk to the carrier? My phone tells me that it is not activated.. help me !