“SIM not supported”, “Invalid SIM”, “PUK”: what each SIM message means
Every common SIM error on iPhone and Android, what it tells you, and whether the fix is a restart, a new SIM, a code from your network or an unlock.
7 minute read Facts checked 25 October 2026
Phones aren’t good at explaining SIM problems. A few words appear at the top of the screen, or in a box you have to tap away, and that’s it. But the exact wording does tell you a lot about what’s wrong, and whether the fix is a two-minute job or a call to your network.
Find the message you’re seeing below. The words differ a little between iPhones, Samsungs and other phones, so look for the closest match.
Try these first
Whatever the message, these rule out the simple causes:
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Restart the phone
Turn it off fully, wait a few seconds and turn it back on.
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Take the SIM out and put it back
Use the tool that came with the phone, or a straightened paper clip, in the small hole by the tray. Check the SIM sits flat with its gold side the right way round.
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Check your account
Make sure the plan is active and paid, and that a new SIM has been activated. Your network’s app usually shows this.
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Try the SIM in another phone
If it works there, the SIM is fine and the problem is this phone. If it fails there too, it’s the SIM or the account.
“No SIM” or “Invalid SIM”
The phone can’t read the SIM, or doesn’t recognise it. This is usually physical: the SIM isn’t seated properly, it’s dirty or damaged, or the tray is bent. Clean the gold contacts gently with a dry, soft cloth and try again.
If another SIM works in the phone, ask your network for a replacement SIM. Most will post one free. If no SIM works in the phone at all, the SIM reader may be faulty, which is a repair job.
“SIM Not Supported”
This is the message people see most when they move to a new network. The phone has read the SIM perfectly well, and is refusing it because the phone is locked to a different network.
On an iPhone you can confirm this in Settings, General, About. Look for Carrier Lock. If it says No SIM restrictions, the phone is unlocked and the problem is elsewhere. If it says anything else, the phone is locked.
The fix is a network unlock, which the original network usually does for free once the phone is paid off. Our guide to checking whether your phone is unlocked explains how to ask for one.
“SIM network unlock PIN”
This is how many Samsung and other Android phones say the same thing: the phone is locked to another network, and it wants an unlock code to accept this SIM.
Don’t guess the code
Some phones allow only a few wrong attempts before they refuse any more, which can make the unlock much harder. Only type in a code that has come from the network that locked the phone.
Ask the original network for the code. Some networks unlock the phone remotely instead, in which case there’s no code to type, and you just restart the phone with the new SIM in.
“SIM Locked” or “Enter PIN”
The SIM card has its own PIN, separate from the phone’s passcode, and it’s been switched on. It asks for it every time the phone starts up or the SIM is put back in.
If you never set one, try your network’s default. It’s often printed on the card the SIM came on, and networks list it on their help pages. You get three tries. If you don’t know it, stop and ask your network rather than guessing.
Once you’re in, you can turn the PIN off. On an iPhone it’s in Settings, Mobile Service (or Cellular), SIM PIN. On Android, search the settings for SIM lock.
“PUK” or “PUK blocked”
After three wrong SIM PINs, the SIM asks for a PUK, a longer code that only your network has. Contact them and they’ll give it to you once they’ve checked who you are. Enter it carefully, then choose a new SIM PIN.
If the PUK is entered wrongly too many times, usually ten, the SIM is permanently blocked. The phone may say PUK exhausted or SIM blocked. Nothing can bring that SIM back, but your network can send a replacement with the same number.
“SIM not allowed” or “Emergency calls only”
Here the phone has read the SIM and tried to connect, and the network has said no. On dual-SIM phones it may say SIM 1 not allowed or SIM 2 not allowed. Other phones show Not registered on network, or just Emergency calls only.
There are a few possible reasons, and the network can tell you which:
- The SIM is new and hasn’t been activated yet.
- The account is suspended, often over an unpaid bill.
- You’re abroad and roaming isn’t switched on for your plan.
- The phone itself has been blocked, because its IMEI was reported lost or stolen or linked to an unpaid contract.
If your SIM works in another phone, the last reason is the one to rule out. That’s where an IMEI check helps.
“SIM not provisioned”
This usually means a brand new SIM that the network hasn’t switched on yet. Activation can take anything from a few minutes to a day. If it’s still showing the next day, contact the network and check the SIM number on your account matches the one in the phone.
When to check the IMEI
Most SIM messages are sorted by your network or a new SIM. Two are about the phone rather than the SIM: “SIM Not Supported” and “SIM not allowed” when your SIM works elsewhere. For those, it helps to know what’s recorded against the phone.
Our diagnosis reads the IMEI and tells you which network the phone is locked to where its records show it, whether it’s been reported lost or stolen, and on an iPhone whether Activation Lock is on. If it’s simply network locked, we tell you how to get it unlocked. If it’s been reported, we tell you that plainly too.
If you’ve just bought the phone second-hand and it won’t connect, our page on a phone that won’t accept your SIM walks through the next steps.