There are a couple of reasons why you may not be seeing your upcoming guest's codes on your Smart Lock.
Your lock is not linked to a listing. You must link your lock to a specific listing so that we know which listing the lock is connected to, and which guests we need to set codes for. Please see this article about linking a lock to a listing.
You have connected a lock via Seam.co and the reservation is more than 72 hours in the future. Seam.co only adds codes to a lock 72 hours before the guest's check-in time.