Backup to external drive stopped mid backup and drive can't be found.

My MacBook Pro is running Sonoma 14.1.1 I keep getting this message while trying to complete a backup. "The backup disk could not be found. Make sure the backup disk is connected or select a different backup disk." I've tried restarting with the backup plugged in and not plugged in. I still get the same message. It's like the system doesn't see the backup drive at all (Seagate 1 TB)