$$PROXYURL$$ at startup, in xml scripts

Hello

(sorry for mistakes, I'm french !)

In my provisionning files, I use $$PROXYURL$$ like this:

expmod1 key18 type: xml
expmod1 key18 value: http://$$PROXYURL$$/phones/xml/dnd.php?user=$$SIPUSERNAME$$&key=expmod1%20key18
expmod1 key18 label: NPD

It works good.
First question: is "expmod1%20key18" correct ? Is it the best choice ?

Second question:
$$PROXYURL$$ seems not working with "action uri startup":
action uri startup: http://$$PROXYURL$$/phones/xml/register.php?user=$$SIPUSERNAME$$&dndkey=expmod1%20key18&stopvoipkey=expmod1%20key17
In xml manual, I read PROXYURL is an "active line SIP proxy", maybe not valid at startup ?
Is there a variable that is always good for indicate sur SIP Server ? (my Asterisk and web server)

Thanks :)