Set max quantity?

Hi, I’m using the below code to limit the maximum quantity per transaction to 4 units. It works fine on the homepage but not on the Checkout page (this plugin’s functionality). Any help would be much appreciated!

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function woocommerce_quantity_input_max_callback( $max, $product ) {
$max = 4;
return $max;
}
add_filter( ‘woocommerce_quantity_input_max’, ‘woocommerce_quantity_input_max_callback’, 10, 2 );
?>

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