Create site-wide coupon on multi vendor store

I would like to add a Free Delivery coupon which I would like to have applied site-wide for all vendors. However I get an error “A coupon must be restricted with a vendor product” when attempting to enter the coupon code during checkout.

I’ve have a look at your forums and I’ve seen this questions being answered about a line of code being commented off (add_filter( ‘woocommerce_coupon_is_valid’, array( $this, ‘ensure_vendor_coupon’ ), 10, 3 );)

However I am not able to find the class-order-manager.php file in the dokan-lite/includes/class-order-manager.php . Am I missing something? Help would be appreciated. I am using Dokan-lite currently.