NetApp volume fails to mount on compute engine -- mount.nfs: access denied by server while mounting

[SHLin]

Problem:
I fail to mount the NetApp volume on the compute instance.

Description (What I have done):
(a) I set up the VPC network private services access following the instruction of 
https://cloud.google.com/netapp/volumes/docs/get-started/configure-access/networking

 

There is some subtle detail here that I could only set this up by force update the VPC network setting because I have set this up before and delete the previous setup. See https://www.googlecloudcommunity.com/gc/Infrastructure-Compute-Storage/Create-NetApp-Storage-Pool-SE... 
I am not sure whether this has any effect.

 (b) I set up the storage pool with the network connection above.
 (c) I set up a nfs volume inside the storage pool.
 (d) I launched a compute engine instance within the same region.
 (e) I followed the instruction of mount disk from the NetApp volume page.

 And I see the error message:
mount.nfs: access denied by server while mounting

I also checked that the firewall setup looks correct. I am not sure what might be wrong. Any suggestions are welcome.