you can’t redirect a form in the way you are attempting to, unless you have some javascript running or the form processing script is already looking for a field named redirect in its script.
without knowing what script you are using or what that script is doing, there is no way to answer your question.
the gist is that HTML forms are processed through an action=”filename.php” attribute on the form tag, or else through a javascript routine taking over when a form is submitted. Either of these call a script (could be the same PHP page the form is on) which then processes the fields that were entered on the form.
what you are doing is passing a hidden field named redirect with a URL as its value, to a forms script. That script then reads the values passed in that hidden field and will redirect the user to the field passed as its value when the script completes. The script must have that feature built in – for example, if you found that code on a forum post and added it in as a result, unless the script you are using expects to receive a hidden field with those values, its not going to redirect just because you have a field named redirect in your form – the script has to be programmed to do that. That is why I can’t answer your question without knowing what the form action script is doing. What you are seeking can easily be done, as long as the script is already programmed to do it.