When you try to use nfs of synology, you meet to this message

“Permission denied”

So, I posting this check list for help you.

1. File permission : Everyone allow access to folder.
   

   Synology have 2-factor permission.
   

   One is Shared Folder, this permission is not important when use to nfs.

   Second is File Station, this permission is important. So if you use to nfs, set to everyone allow.

2. Allow connection from non-privileged ports: many case is need to enable

   When you set nfs, you need to check this option enable.
   

           Allow connection from non-privileged ports
   

   Another option you can choice your face.
   

3. Offer to nfs share.

   You can check nfs list on server easily.
   

   showmount –e <serverip>
   

   And you try to mount to nfs this command.
   

   mount <serverippath> <drivepath>
   

   If you want to use mount command you need to install NFS Service
   

   Control -> Program Add/Remove -> Windows feature
   

    

4. Finally, Disable File Service <Windows File Service>, <Mac File Service>
   

   Now you need to use nfs, so another service disable for test.
   

   And try to mount again.
   

PS. NFS Client Tool Help for test easier

https://www.softpedia.com/get/Network-Tools/Misc-Networking-Tools/NFS-Client.shtml