How to setup VPN passthrough on the Arris BGW210

I have the Arris BGW210 as the main modem/router and also a Asus AC86U.

I would like to setup the 86U as the VPN router but the problem I have it wont connect to a UDP file. only a TCP, VPN support told me most likely the BGW210 is causing the issue.

What should I do now,

Thanks