My iPhone XR doesn’t support my sim card

When you say the phone works when it doesn't have a SIM card, you're not saying you can make phone calls or anything, just that you can open the phone, maybe connect to wireless and run apps, right?

Anyway, that's beside the point, which is that most likely the phone has a SIM lock; in other words, it's tied to a specific carrier like AT&T or Verizon and must be unlocked by that carrier before it can be used on other networks like yours.

First step is to use some of the online tools available to find out what carrier your phone is locked to. One that I've had good success with is IMEI CHECK - IMEI Number Checker Online. Put in the IMEI number of your phone into the website and it should tell you whether there's a SIM lock on your phone and hopefully what carrier it's locked to. If that one doesn't tell you, search for other SIM lock checkers online and try a variety of them until you get an answer. You can usually find one without having to pay for it, so don't be quick to pay for that service.

Once you know what carrier it is locked to, if that's the case, you can check with them on the phone's status and request that they unlock it. In most cases they're obligated to unlock a phone unless it's been financed and there's still an unpaid balance on it. If that happens there's not much you can do about it, as they won't take payment from you since you're not the owner (at least in their eyes) so you can't pay off the balance and get it unlocked.

Give that a try and let us know what you find out about your phone.

Oh, and if it is SIM locked, one thing you can do even if it has an unpaid balance is that you can sign up for an account on that carrier. The phone will still be usable even though there's money owed on it; the only consequence will be that you won't be able to unlock the SIM card.

I got an iPhone 6S Plus for my granddaughter, but neglected to check the SIM lock status when I bought it. After completely rebuilding it I realized it couldn't be used on my network because there was an unpaid balance with AT&T. I was able to give it to my son-in-law though, since he used AT&T as his carrier and it worked fine for him.