Setup your Shopify zones and enable Postcode Shipping rates
To do this you'll need to create zones in Shopify and select Postcode Shipping as the rates provider.
Even if you already have your zones set up in Shopify, you'll still need to enable Postcode Shipping as the rates provider, so follow along with this guide.
Set up zones in Shopify
From your Shopify dashboard, navigate to Settings > Shipping and delivery.
Click Manage rates.
Scroll down to the 'Shipping to' section.
Here you will add zones which reflect those you have set up in Postcode Shipping.
Notes: If you already have your zones set up from before you installed the Postcode Shipping app, you can work with the zones you already have. Skip to the next part, Enable Postcode Shipping rates, below.
Click Create shipping zone.
Give your zone a name and select the countries that will make up the zone.
Click Done when you are ready.
Make any other zones you need.
Enable Postcode Shipping rates
With your Shopify zones setup, you need to enable Postcode Shipping as the rates provider.
Click Add rate.
If you already have rates set up from before you installed the Postcode Shipping app, delete these and add a new rate.
This is the important part. Choose Use carrier or app to calculate rates, and select Postcode Shipping (Rates provided by app).
Do the same for any other zones.
Note: you'll only need to do this once for each zone, as you're not actually adding rates, you're just connecting the Shopify zones to the rates you've already created in the Postcode Shipping app.
The last thing you need to do is Save your changes.
Now you've setup your Shopify store to automatically use any rates you create in Postcode Shipping. If you haven't already done so, go ahead and create your zones, ranges and rates in Postcode Shipping.