如何将APEX参数值传递给外部URL

In my APEX application I have created a button that should carry a parameter value of the current page to an external URL

The optional URL redirect target is set to URL of PHP file.

I have set the URL target for the button to http://[URLNAME]?sid=:student

From what I understand the APEX variable is not substituted.

Can anyone tell me how it CAN be substituted ?

Many thanks

To reference page or application items using substitution variables:

1. Reference the page or application item in all capital letters.
2. Precede the item name with an ampersand (&).
3. Append a period (.) to the item name.

For example, you would refer to an application item named F101_STUDENT in an HTML region, a region title, an item label, an URL link, or in any of numerous other contexts in which static text is used, for example:&F101_STUDENT.

For your case you can use http://[URLNAME]?sid=&STUDENT.

When the page is rendered, Application Express engine replaces value the substitution string with the value of item F101_STUDENT.