Why can I not switch my SIM card from my iPhone 7 to an 11?

Are you following the instructions correctly? Refer to: Remove or switch the SIM card in your iPhone - Apple Support

denisemp1 wrote:

Why can I not switch my sim card from my iphone 7 to an 11?

Shouldn't be an issue if you're using the same phone carrier, but you can request a new sim for your 11 from your phone carrier.

What happens when you try?