Here is a check list if you encounter any issue to configure or access your folder on Synology from your Zappiti Player.
1) Is the folder shared on the local network ?
2) Are the permissions set on "Read/Write" option for the admin user ?
3) In "File's service" > "SMB/AFP/NFS", is the SMB share enabled ?
4) In the same section, in "Advanced parameters", is the "Minimum SMB protocol" set on "SMB 1" ?
5) When you enter your credentials to access the folder from your Zappiti Player, do you use the admin's credentials ?
Is there an application or software such as "firewall" or antivirus or other that could restrict communication between devices ?