SIM is not Supporting
My sister is from USA and now a days visiting India but she is not able to use I phone 7+ while we insert India service provider SIM it shows SIM is invalid message
iPhone 7 Plus
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It means that her iPhone is carrier locked.
She has to contact her carrier and ask to unlock her iPhone for use with different carriers.
More info here: How to unlock your iPhone for use with a different carrier - Apple Support