This is the solution I did, to get ExpressVPN working in Manjaro:
Hope it can be to some help 
1. Terminal:
wget https://www.expressvpn.com/expressvpn_release_public_key_0xAFF2A1415F6A3A38.asc
gpg --import expressvpn_release_public_key_0xAFF2A1415F6A3A38.asc
2. Installed expressvpn in Pamac
3. Terminal:
sudo cp /usr/lib/expressvpn/expressvpn.service /etc/systemd/system/expressvpn.service
sudo systemctl daemon-reload
sudo systemctl start expressvpn.service
expressvpn activate
My only question is why there is two buttons (Red and Green) in Pamac installation ?