SIM Support
Please my iPhone 5s does not support my current SIM card. Any help
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Why not? What happens when you insert the SIM card exactly?
If you get the dreaded "Sim not supported" message, it means the iPhone is locked to a service provider that is different to the one the SIM card you inserted is for. Only the servicer provider it is locked to can unlock it.
click here ➜ How to unlock your iPhone for use with a different carrier - Apple Support
If something else is happening, please explain in as much detail as possible.