iPhone is not detecting SIM card
sim card inserted phone not showing has SIM card in it
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Remove your SIM card from the SIM card tray and then put the SIM card back. ... Make sure that the SIM tray closes completely and isn't loose. If you use a SIM tray from a different model iPhone, iPad, or from another phone manufacturer, it might not fit properly.
If you see 'invalid SIM' or 'no SIM' on your iPhone or iPad ...
Learn what to do if you see a SIM not supported alert.