Urbackup cliend - waiting for server issue

Hi guys!
I have urbackup server on ubuntu and windows client. I run the cat /var/log/urbackup.log and I am getting the error
WARNING: Upgrading database to version 59
2022-05-31 18:13:48: WARNING: Done.
2022-05-31 18:13:48: WARNING: Creating file entry index. This might take a while…
2022-05-31 18:13:48: ERROR: No permission to access “/backup/urbackup_tmp_files”
2022-05-31 19:01:52: ERROR: Error sending client access key
2022-05-31 19:18:33: WARNING: Shutting down (Signal 15)
2022-05-31 19:36:58: ERROR: Error sending client access key
2022-05-31 19:47:59: WARNING: Shutting down (Signal 15)

Can someone explain me why I am getting this error when I’m doing the full file backup it only says “Waiting for server”. Please do let me know where to check and hat is the solution for this error.