I have added the following OpenVPN server in the router.

And I have created two users like this

I have exported the OpenVpn certificate and installed the same in the OpenVpn connect Client. (remote is ej in file is my public ip)

When I connect the first client there are no problems, it connects correctly

But if there is already a client connected to the OpenVpn tunnel and I try to connect another one, I get the following error

I don't understand where the problem could be. I can only use one client, it doesn't matter which one it is. If I connect computer A first and then computer B, computer A connects correctly and the connection works perfectly and computer B gives the error and vice versa.

Any ideas? I have tried with another Omada Er605 and other equipment and the problem is exactly the same.

Version of OpenVPN Client: