I permit to come back to you concerning this request, I invite you first to restart the NFS ACL of access to the backup storage in relation to the IP address of your dedicated server.
If you continue to encounter errors not related to an NFS setup, I invite you to return the following commands via your dedicated server
mount
mount -t nfs -o nfsvers=3 HostName:/export/ftpbackup/ServiceName /FolderMount -vvvv
HostName : name of yout backup storage
ServiceName : name of your dedicated server
FolderMount : folder when you want to configure your mount point