Magento’s Free Shipping Promotion Rule is not working with some 3RDparty shipping modules.
Solution:
This issue can be resolved by adding some codes to the extension. For example, in Fontis Australia, the below condition was missing.
if ($request->getFreeShipping() === true || $request->getPackageQty() == $this->getFreeBoxes()) {
$shippingPrice = ‘0.00’;
}
Adding this code in the Shipping carrier extension’s model file, it will support the Promotion rule set for free shipping.