Permission problems with Windows 10 Pro - ReadyNAS 2120 v2 - Office 365

Start by allowing everyone access in the file permissions (and re-check the "grant rename" box).  Then reset the file permissions (which will apply them to all the files and subfolders in the share).

Then move to the Network Access tab, and disable everyone and anonymous access there.  Then either set the group permissions for the AGTest user's group (likely users) to read/write, or give the AGTest read/write access.  If you intend to have lots of users access the share, then it is simpler to use group access (and put the individual accounts in appropriate groups).

To have access, users need to have both network access and file access. In many (IMO almost all) situations, it is better to manage share-level access using only Network Access, and leave file access set to allow everyone read/write.  That is administratively simpler. 

One aspect here is that users with write access can change the file permissions from their PCs, but changing network permissions requires admin access to the NAS.  So you do choose to restrict access using the file access tab, you also need to restrict access on the network access tab. 

One exception to using only network access for management would be if you intend to allow some users ssh access to the NAS, and you need to restrict their access when they are using ssh.