Versions higher than OpenVPN 2.4.0 with OpenSSL 1.0.2k of are restricted to 3499 characters on the ASUSWRT- Merlin web interface. Our CA.key is more than 3499 characters long and have 2 parts.
Earlier versions of OpenVPN would import the long string using ASUSWRT-Merlin without issue. However, the newest router firmware contains newer OpenVPN and is not able to import the ca key via import nor allow you to manually enter the correct key via the web interface.
A walk around to this is access your router via SSH and manually copy the whole CA.key directly.
This will require a little knowledge of linux command. We assume you know what you are doing as installing 3rd party firmware requires you to flash and have some command line knowledge
Here are the steps;
1) SSH into your router using putty or any SSH application. (The username and password is the same as how you login to your router via the web interface)
2) Locate the directory ~/jffs/OpenVPN
There should be a file named vpn_crt_client1_ca (if client2 is used, vpn_crt_client2_ca)
3) using the vi OR nano function edit the vpn_crt_client1_ca file
4) Paste both parts of the CA.Key key larger than 3499 characters and save. Starting from ------BEGIN CERTIFICATE----- to -----END CERTIFICATE---- (there are two parts of this;copy both of them).
Note: For inline ovpn files; it should be the line starting after <ca> and before </ca>
This should allow you to connect to the server on your Router.