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.

[SHLin]

If someone runs into the same problem, I solve this by setting up the export rule. It is not specified on the NetApp document on Google Cloud website, but the instruction below is given in the "Getting Started with Google Cloud NetApp Volumes" training.