Why is the ip address of the vpn server not coming?

Question

openvpn

Compiled firmware for TP-Link WR740N from OpenWRT sources. Everything works, including OpenVPN (I collected it for this).
But it only works with the vpnbook.com config. When I take the config from the vpngate.net site, the router cannot get the ip address in any way. By ifconfig, the tun interface appears, but it has no ip address => no vpn connection. Who can faced similar?
And yet, what to register in the settings to log in by key, and not by password? I suspect that auth SHA1, but I'm not sure.