OpenBox rc.xml : Adding a keybind to Open Terminal

I am trying to add a keybind into my ~/.config/openbox/rc.xml file but to no avail.
This is what I have, trying to open an urxvt session with the mod4 key + r.
<keybind key="W-r">
<action name="Execute">
<command>urxvt</command>
</action>
</keybind>
What changes need to be made to fix this?