Undefined index in PHP

Good day!

I am having the following error in my code:

if (!$_POST['SUBMIT']){   //ERROR: Undefined index
?>
    
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    }
    else {
    //code here
    }
?>

How can I remove the error above? Thank you.

Answer

It should be a notice and not an error.

To fix is you'll have to check whether $_POST['submit'] is set:

if(!isset($_POST['submit'])) {
    ...
}