Unless you have a MBR1400v2, AER21X0, AER31X0, IBR11X0, or IBR600 Cradlepoint, your Cradlepoint does not support it.
Your TP Link router also doesn't support VPN software, from a quick google. Your best option would be to find a router that supports it or do this with a Raspberry Pi...
GhostVPN with Raspberry PiI set my Cradlepoint to IP passthrough, use an older router that supports VPN, and set my Orbi's to be access points only and not to be a router. All I had to do was follow a walk through on the NordVPN website, copy paste from the NordVPN sites my user name/password, a config file, and turn it on.
I'm sure you can find a list of GhostVPN compatible routers. The software my router has is called NetDuma OS and DumaOS is currently available on the Netduma R1 (what I have) and NETGEAR Nighthawk Pro Gaming XR500, XR700, XR300 and XR450.