There might be an issue with iPhone devices on the iD Mobile network in areas where their 3G network service has been switched OFF, @mantasbu. 

Others have posted about similar experiences here in this online public forum.

So how can I make my SIM card work on Apple iPhone 16 Pro?

Okay @mantasbu, the following steps might help fix this, especially if the iD 3G network service has been switched OFF in your area.

• Turn OFF your iPhone, and carefully remove the iD SIM. 
• Wait for at least 30-minutes, with the device OFF and the SIM removed.
• Carefully insert the iD SIM in the SIM tray of your device, and power ON.

I confirm that this did not work. What else could I do?

You need to enter your mobile number into the devices settings. Been mentioned here time and time again. 

Sometimes it shows 4G and sometimes it shows 5G so I don’t think it is 3G.

How could I enter my mobile number into the device settings?

Using another SIM card (giffgaff) works without doing any other additional steps.

Open settings, select apps, scroll down and select phone, and where it says “My number” type your number starting with a 0(zero). Then click save.

This worked on my iPhone but I had to go via settings / apps / phone / my number. Good luck 

@WelshPaul thank you so much, it solved my issue.

Hi @mantasbu @EM53,

Glad to hear that @WelshPaul could assist.

Please get back to us if you require further assistance.

Kash