Disabling Woocommerc Downloadable Images from Being Watermarked

I’m building a stock image website, and I want the previews to be watermarked but not the downloadable full quality images.

From this page on Dfactory’s website, I got this code

function custom_iw_watermark_display($attachment_id) {
	// do this in admin only
	if (is_admin()) {
		// get uploaded file url
		$attachment_link = get_attachment_link($attachment_id);
		// check if file path points to woocommerce upload folder
		if (strpos($attachment_link, 'woocommerce_uploads') !== false) {
			// if it does, disable watermarking of this specific image
		    $attachment_id = false;
		}
	}
	return $attachment_id;
}
add_filters('iw_watermark_display', 'custom_iw_watermark_display');

But it returns and doesn’t even save it

Your PHP code changes were rolled back due to an error on line 137 of file wp-content/themes/hello-elementor-child-theme/functions.php. Please fix and try saving again.

Uncaught Error: Call to undefined function add_filters() in wp-content/themes/hello-elementor-child-theme/functions.php:137
Stack trace:
#0 wp-settings.php(591): include()
#1 wp-config.php(99): require_once('/home/stockavn/...')
#2 wp-load.php(50): require_once('/home/stockavn/...')
#3 wp-admin/admin.php(34): require_once('/home/stockavn/...')
#4 wp-admin/theme-editor.php(10): require_once('/home/stockavn/...')
#5 {main}
  thrown

Thank you!