On the EdgeRouter, make changes where appropriate…

set interfaces openvpn vtun0 firewall in name OpenVPN-Mobile
set interfaces openvpn vtun0 local-host xx.xx.xx.xx
set interfaces openvpn vtun0 local-port xxxxx
set interfaces openvpn vtun0 mode server
set interfaces openvpn vtun0 openvpn-option --mssfix
set interfaces openvpn vtun0 openvpn-option '--cipher AES-128-CBC'
set interfaces openvpn vtun0 openvpn-option '--auth SHA256'
set interfaces openvpn vtun0 openvpn-option --float
set interfaces openvpn vtun0 openvpn-option --duplicate-cn
set interfaces openvpn vtun0 openvpn-option '--fragment 1400'
set interfaces openvpn vtun0 protocol udp
set interfaces openvpn vtun0 server max-connections 10
set interfaces openvpn vtun0 server push-route 10.10.10.0/24
set interfaces openvpn vtun0 server subnet 10.10.10.0/24
set interfaces openvpn vtun0 tls ca-cert-file /config/auth/openvpn/ca.crt
set interfaces openvpn vtun0 tls cert-file /config/auth/openvpn/server.crt
set interfaces openvpn vtun0 tls dh-file /config/auth/openvpn/dh.pem
set interfaces openvpn vtun0 tls key-file /config/auth/openvpn/server.key

Example client config file…

client
tls-client
remote remote.hostname.here
port xxxx
proto udp
dev tun
pull
cipher AES-128-CBC
auth SHA256
fragment 1400
mssfix
float
<ca>
ca certificate file contents here
</ca>
<cert>
pem certificate file contents here
</cert>
<key>
pem key file contents here
</key>