Unable to connect two routers for VPN passthrough with primary router
I have a TPlink C7 1750 primary router (192.168.0.1) where I have enabled all passthrough checkboxes. I purchased another TPlink router to use as VPN only router with IPaddress 192.168.0.100 and disabled DHCP on this. Then I connected primary router and VPN router but an ethernet from LAN of primary to WAN/LAN of VPN router. Upon going to WAN in the primary router and changing it to PPTP and entering the PPTP IPaddress and username/password of VPN provided, it does not connect to the VPN server of the provider. I am unsure if it is configuration issue of primary router, where I checked that PPTP passthrough is enabled, or VPN router I am setting up.
please help in configuring the routers correctly.