iPhone 6 - sim not Valid

You are not talking to Apple.

Even if you were, Apple can't help you with this.

Your phone is locked to a cellular carrier other than the one you are trying to use.

ONLY the carrier it is locked to can unlock it.

Get a sim from your carrier. The same people you pay each month for service.

Your phone is carrier locked. You need to contact your carrier to get it unlocked.

Do as we have all suggested and contact your carrier.