Your Shopify store will require Carrier Calculated Shipping to use the Postcode Shipping app. Some important points about carrier shipping:
Access to the carrier shipping feature is provided by Shopify, and is available by default on Shopify Advanced and Plus plans.
Your Shopify store plan needs to be billed annually to ensure you have access to carrier shipping.
If you're using the regular Shopify or Shopify Basic plans you are still able to access carrier shipping, simply contact Shopify Support (firstname.lastname@example.org) and request the Carrier Calculated Shipping option be added to your account. Note: your plan needs to be changed to annual billing before you make this request.
From your Shopify dashboard click Settings > Plans & Permissions.
Here you can view your current plan. If your plan type says 'Monthly' next to it, you will need to change your plan to be annually billed. You will receive a 10% discount on your total Shopify plan price by pre-paying the subscription.
Click Compare plans.
From the information box at the top of the screen, choose Change your billing period.
In the 'Billing cycle' section, change your selection to an annually billed option.
Click Start plan.
Once you've set your account to be billed annually (and, if needed, requested access to the carrier shipping feature from Shopify Support) you are now ready to install the app. To find out how read our article Installing Postcode Shipping.