I´m using a TP-Link MR200 as mobile LTE-AP in my car. Works fine, but I cannot establish a VPN Connection with my Phone to my UniFi Homenetwork trough the TP-Link WiFi. Other Routers with same LTE-SIM can do this, so my ISP doesn´t block this but I want to use the TP-Link because this one has Connectors for external Antennas.
Could anyone help me to configure the Router to let passthrou my Phone to the UniFi USG at home?
I installed LEDE Reboot r1811 on the TP-Link.
It might help if tell us exactly what type of VPN you run from the phone to the Home router. The title says "from openwrt", because other routers work - you mention PASSTHROUGH ... I take it you mean "through remote openwrt"???
If so, best to clarify thread title 
Just saying "other routers work" is oversimplifying, especially without knowing the protocol used.
Have you done any general searching on VPN client connect problems through an openwrt router?
Thanks for your hints. I´ll try to specify my Problem with my limited english writing/speaking skills 
I´m using the TP-Link MR200 as LTE-Router in my car. With my Android cell phone I try out of the Wifi of the MR200 to establish a VPN connection to my L2TP server at home (Ubiquiti UniFi Security Gateway). The L2TP/IPSec VPN connection is set up on both sides (Phone and @home) and works via LTE or other WiFi, but not via the WiFi of the MR200 with Openwrt nor Original Firmware.
I used the SIM which is normally in the TP-Link in a ZTE MF910 LTE-Router to exclude ISP restrictions. It worked well.
So I think, there is a configuration Problem with the MR200 but I doesn´t have a clue which. Maybe Firewall? I really need help with it 
@anon50098793 What do you think, I should use as Thread Title in this case?
To your question: I googled a lot, but I found nothing what could help me, so I tried to ask here.
The title "No VPN connection from openwrt to UniFi USG" is innacurate. The quotes as stated by you above should do... or just change FROM to THROUGH.....
Really?
https://www.google.com.au/search?q=openwrt+l2tp+ipsec+passthrough+site:forum.archive.openwrt.org
Pro tip: tcpdump on the router interfaces is useful. As are the logfiles of the l2tp server and client .... Also, the manual/documentation for the UniFi USG should contain the some basic instructions regarding this.....
Really! And I found nothing helpful. I will check in the results you kindly googled for me.
I´m not only a noob in writing english. I´m also a noob in configure firewalls, so I ask for more specific help.
i.e. how do I get a tcpdump on the router interface?
USG is not the problem (imho) because it works without openwrt.
?
nsfw or why did you withdraw your post?