Restore Filelistonly command fails

I am trying to restore the file from NAS server I am getting a below error message.

I have also checked mapping the server local and trying to restore.

Msg 3201, Level 16, State 2, Line 2
Cannot open backup device '.M:\....bak'. Operating system error 3(failed to retrieve text for this error. Reason: 15105).
Msg 3013, Level 16, State 1, Line 2
RESTORE FILELIST is terminating abnormally.