Cannot access devices behind OPENVPN server when using GL-MT300N-V2-d2a OPENVPN client

Hello there,

I recently bought a GL-MT300N-V2-d2a to use as an openvpn client.
I have an openvpn server running on a raspberry pi in a remote location.
I have no problems using the GL-MT300N as an OPENVPN client for accessing the internet however I cannot access local devices behind the openvpn server.
I have several android phones (using wifi on the same lan as the GL-MT300N router, connected to the main broadband router, not via the theGL-MT300N router) with openvpn client software and I have no problems accessing the local LAN behind the openvpn server. Does anything need to to be changed in the GL-MT300N settings to access local devices behind the openvpn server? Can anyone confirmed if they have managed to get this working? Thanks.

Could you please draw a network topology with IP address for me? Maybe it causes by the subnet issue.