Kudos on such a great plugin, It is really appreciated.

I am attempting to add a form specific cookie aftr my for has submitted and has validated.

for a test I haev set up the following function in the my-functions.php file.

function my_cforms_action($cformsdata) {
    $formID = $cformsdata['id'];
    setcookie('airConditioning', '$formID');

}

at the end of the submission I get this error-

Warning: Cannot modify header information – headers already sent by (output started at my-file-path/wp-content/themes/default/header.php:8) in my-file path/wp-content/plugins/cforms/my-functions.php on line 20

I cannot figure out why I keep getting this error.  any Ideas