Unable to complete backup

[hodaka]

Newly purchased F2-212, I have completed the initial configuration successfully, and am able to connect to the unit and manually copy large files successfully.
Time Machine sees it as an available drive, connects to it, and starts the backup process. But it will not complete it. I have tried afp and smb. A file is created on the 212, but again, will not complete the backup. I’ve been fighting it for a couple weeks now.

F2-212 is running 5.1.37
Mac is an M1 iMac, on Sonoma

I am also backing up to a Time Capsule, which is still running brilliantly, I might add. I was hoping this Terra Master NAS would replace it so I am not running on borrowed time…