This is the most common culprit. If the client’s IP address or AD Site isn't part of a defined Boundary Group, it won't know which Distribution Point (DP) or Software Update Point (SUP) to talk to. Microsoft Learn Verification: LocationServices.log on the client. Look for WSUS Path= to see if it’s actually finding a server.
In :
The error code 0x87d00215 is a generic error code that can occur due to a variety of reasons, including: Failed To Get Targeted Update Error 0x87d00215
Are you seeing any in the DataTransferService.log ? This is the most common culprit