I bought a new iPhone. I want to put my wife's sim card into my old phone. Her iphone is an iPhone 6+. The iPhone I want to put it into is an Iphone 7+. I tried it and it doesn't work.
Are both phones from the same company? Do you have a payment plan for either phone line? Most likely the sim is locked to the hardware from the provider. Usually, they only allow swapping if its a replacement or upgraded device from them.