Quick answer: if the SIM or eSIM is new, give it time to activate, then restart your phone. If it's not new, check your plan is active and the phone is unlocked, reseat a physical SIM, and check for a carrier settings update. If none of that works, contact your network.
What the alerts usually mean
- SIM not provisioned: the network hasn't activated the SIM yet. You'll often see this with a new SIM or straight after switching.
- No SIM: the phone can't detect a SIM at all, perhaps because a physical SIM isn't seated properly.
- Invalid SIM: the phone sees the SIM but can't use it. A locked phone with another network's SIM is a common cause.
Fixes, in the order Apple recommends
Check your plan is active
If you've just joined or switched, activation can take a little while. Your new network's text or email usually says when it's live.
Check the phone is unlocked
On iPhone, go to Settings > General > About and look for No SIM restrictions. On Android, see our unlock check.
Restart your phone
A restart makes the phone read the SIM again and is often all it takes.
Check for a carrier settings update
On iPhone, go to Settings > General > About and wait a few seconds. If an update is available, a prompt appears.
Reseat a physical SIM
Take the SIM out, check for damage and put it back, making sure the tray closes fully. Apple warns that a tray from another phone model may not fit properly.
Switch the SIM off and on (Samsung)
Go to Settings > Connections > SIM manager, switch the SIM off, then back on.
Try another SIM
If a friend's SIM works in your phone, the problem is your SIM. Ask your network for a replacement.
Contact your network
For eSIM problems, your network needs to fix it. Have the error message, your number, your account PIN and your phone's IMEI ready (dial *#06# to see it).
If no SIM works in the phone, it may need repairing. Apple and Samsung both offer repair services.
Ready for a better deal?
SIM-only plans on every big network from £5 a month. Keep your number when you switch.
FAQs
How long does it take for a new SIM to be provisioned?
Often minutes, but it can take longer when you're switching networks and moving your number. If it's been more than a day, contact your new network.
Can a locked phone cause "Invalid SIM"?
Yes. A phone locked to one network won't accept another network's SIM, and often shows an invalid SIM message. Unlocking it fixes this.
Will restarting delete my eSIM?
No. Restarting doesn't remove an eSIM. Only deleting the eSIM in settings, or erasing the phone, removes it.
Is it my phone or my SIM?
Try your SIM in another phone, and another SIM in your phone. Whichever fails in both places is the problem.
Steps checked on 2 November 2026 against official help pages: Apple: No SIM or Invalid SIM · Apple: eSIM setup help · Samsung UK. Menu names can vary slightly by phone model and software version.