Do the iPhone 4 and iPhone 6 use the same type of simcard

No.

The iPhone 4 uses a micro sim and the iPhone 6 uses a nano. There are other differences as well.

Hi

If it,s a multi simcard you can push the centre out to change to a nano simcard.

If not ask your network provider for a simcard replacement.

Cheers

Brian 🇬-1F1E7;