Problem accessing PayPal form variable

I'm trying to get this post开发者_StackOverflow社区 value of this variable, but I can't access it.

<input type="hidden" name="on0" value="url">

I've tried $_POST['on0'] but it's not working

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If the form action is POST then using $_POST['on0'] should work. (If the action is GET, you'll need to use $_GET['on0'].)

If neither of these are working, then it's likely that there is no value stored (i.e.: that the "url" is blank) or that the element name isn't "on0".