first install v2ray core

sudo pacman -S v2ray

then install v2rayA as client 

download the file with name like this

installer_archlinux_x64_2.2.7.4.pkg.tar.zst

then with command line run

sudo pacman -U ./installer_archlinux_x64_2.2.7.4.pkg.tar.zst

then you can control it from http://127.0.0.1:2017/ address