Unlocking

Yes, it doesn't make sense.

If it works using the original SIM card, contact the previous carrier. Only that carrier can unlock that device, if you're eligible, as per this support article:--> How to unlock your iPhone for use with a different carrier - Apple Support

Neither we, just users like you, nor Apple can help you.

Regards and best of luck.

Giulio

🇮🇹

If you're sure that that device is "unlocked" and SIM free, contact your carrier and ask them for a spare SIM card (Very rarely it can happen that the SIM tray / holder is broken. In this case, have your iPhone checked at an Apple Store or AASP)

Regards

Giulio

You can also get confirmation from Apple support (800-MY-APPLE) on whether your phone is locked to a carrier or not by providing your serial number. If your phone was unlocked previously by someone other than the carrier and you restored the phone recently, there is a good chance that it became re-locked to the old carrier. Advice from ProustGiulio to contact the carrier is good advice.

Exactly what message are you seeing?

Where was the phone purchased?

🇨🇦

Unfortunately, the Carphone Warehouse does not sell unlocked iPhones. As with most such instances, the SIM Free iPhone, sold by these dealerships will lock to the first cellular provider used.

You are welcome