Finally I got it..
I manage with this mod to post the clients MAC-address to an external webserver doing the PayPal and Radius processing.
Here is the solution:
In /usr/local/captiveportal/index.php goto line number 174 and look for:
portal_reply_page($redirurl, "login");
Comment out this line and put in your own redir-command with client MAC-address:
/* display captive portal page */
/* portal_reply_page($redirurl, "login"); */
/* PUT IN YOUR OWN CODE FOR REDIRIECTION TO AN EXTERNAL PAGE */
echo <<<EOD
<html>
<head>
<title>Wireless from GateLink | Hotspot</title>
</head>
<body onLoad="document.gatelink_form.submit();">
<form method="post" action="
http://your.domein.name/paypal-order.asp" name="gatelink_form">
<input name="mac" value="$clientmac" type="hidden">
<input name="redirurl" value="$orig_request" type="hidden">
<center>Processing Information . . . </center>
</form>
</body>
</html>
EOD;
/* END CUSTOM REDIR */
Happy Hotspotting
Paal Soelvberg