Dodge Challenger seat belt not locking

We’re borrowing my husbands parents vehicle at the moment since ours isn’t working. It’s a Dodge Challenger and when I go to put my daughter car seat in the seatbelt will not lock with it. The base is in our vehicle which is getting fixed at the moment so we don’t have it. Can anyone help me with this? We have a long drive today and I’m worried about the seatbelt not locking around her car seat.