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?
6) Do you use any app or software that could make the dialog between the two devices erratic or impossibe?