Sim Not Valid

If you were using the iPhone previously with this sim card, it points to it having been hacked to unlock it for use with sim cards from carriers other than the one it was locked to.

if you recently updated it or restored it, it would have wiped the hack, and locked the phone back to its original carrier.

The only way to officially unlock it is to have the carrier it is locked to, unlock it. You will have to do what the message says and contact the carrier it is locked to, to get it unlocked.

You can call Apple first, and they can tell you what carrier it is locked to.

See here: How to unlock your iPhone for use with a different carrier - Apple Support

I take it you are seeing a much longer message than just sim card invalid. You need to contact the cell service provider that holds the lock and find out what their unlock policy is and if you quality. If you don't know who it is locked with call AppleCare and give them the model and serial numbers and tell them you just want to know if the phone is carrier locked and if yes who it is locked with.

I'm from the Philippines, and I've bought this iphone 6s+ online 2 years ago. It says here "SIM NOT VALID" The sim card that you currently have installed in this Iphone is from a service provider that is not supported under the activation policy that is currently assigned by the activation server. This is not a hardware issue with the Iphone. Please Insert another SIM card from a supported service provider or request that this Iphone be unlocked by your service provider.

However, I did insert a lot of sim cards, but none of them worked.

Any idea how to solve my issue?

Thank you!

You will need to contact your network provider who can unlock the phone. You may need to pay a fee.