This Article Applies to:
All the Wi-Fi Routers that support VPN Client, such as Archer AX20, Archer AX21, Archer AX90, etc.

Issue Description/Phenomenon:
The Wi-Fi Routers that are being discussed here are the models support VPN Client, which allows users to connect to a VPN server without the need to install VPN software on each device. If you are unable to connect to a VPN server when trying to configure the VPN client on the TP-Link router, this article provides some suggestions that may help you out.

Troubleshooting Suggestions & Solution:

Step 1 
Ensure you can successfully connect to the VPN server using a third party VPN client software like OpenVPN Connect on the local PC/Smartphone. This can ensure the .opvn file is configured and exported correctly. 
For example, If you are trying to connect NordVPN, please don't use NordVPN App since it doesn't require the .opvn at all.

Step 2
If step 1 is confirmed good, but it still fails to connect to the VPN server when uploading the .opvn file into the TP-Link router, be sure the router's firmware is up-to-date. You can check for the updates on the Tether app or on router web GUI, or you can download it from the local official website then install it manually.

Step 3
If it still fails, please check the size of the VPN configuration profile you are trying to upload to the router, how large that file is. You may download and install the Notepad+ application to delete the useless comment in the profile if that is too large, then try uploading it into the router again.

Step 4
It's also suggested to try TCP protocol on the VPN server if it's currently using UDP, then save the file and upload it into the TP-Link router again to check if that works.

If the VPN connection still fails, please email support.forum@tp-link.com with the subject [Forum ID 270268] VPN Client is not working, or leave a comment below. In either case, be sure to provide the following information:
1. Model number, hardware and firmware version of your TP-Link Router.
2. What kind of VPN server you are connecting to?
3. What kind of VPN type you are choosing on the TP-Link router, OpenVPN, or PPTP VPN?
4. What kind of VPN Client software you were using on the local PC or phone when it is connecting fine? If you're connecting to an OpenVPN server, please test and make sure you can connect to the server with a third-party software, such as OpenVPN Connect.
5. Which step did you stuck in, any error message or screenshot?
6. Troubleshooting you've done before, and be sure the .opvn file is included when emailing to support.

Related Articles:
If you are not familiar with the VPN Client configuration on the TP-Link router, visit How Do I Use VPN Client to Access a Remote VPN Server.
If you want to check which model supports VPN Client, visit Routers supporting VPN Client.

If you are unable to connect CyberGhost OpenVPN Server, please try Manually create the unified format for OpenVPN profile(CyberGhost OpenVPN Server)

-------------------------------------------------

Have other off-topic issues to report? 
Welcome to > Start a New Thread < and elaborate on the issue for assistance.