I can’t use any sim other than zain . Saying that sim not supported

If you purchased your phone through Zain, its possible that the phone is 'locked' to that carrier.

Carriers often sell phones at a discount, making up the difference over the life of a contract (e.g. 12- or 24- months).

The carrier can unlock the phone, which will allow other SIMs to be used. You'll need to contact Zain and ask them to do that.

That means that the phone is locked to that carrier. you will have to ask them about their unlocking policy.

Ask zain to unlock the phone. Nobody else, not even Apple, can unlock it.

You can ask your carrier to unlock the phone, but they are under no obligation to do so. In some cases, if the carrier may agree to unlock the phone for a fee.