By default, Shopify’s carrier for Australia is set to Sendle.

The rest of this articles explains how to use other carriers and bring your own rates, as well as dynamically showing customers the freight costs at checkout. You can even add a margin to freight costs.
If you haven’t already done so, make sure your Shopify store is linked to EIZ, or follow the instructions found here: https://eiz.zendesk.com/hc/en-us/articles/4403223177113
Next, login to your Shopify store and select Apps from the left panel menu.

Select the EIZ Shipping Price Calculator to open and edit its features.

From your available carriers, simply select the carrier you would like to appear in your checkout.

Your customers will now be able to see your selected carrier with pricing quoted at the checkout.

All orders placed through your Shopify store will be synced to EIZ, where you can fulfill them in bulk. All it takes is a few clicks: create shipments, assign carriers, generate labels, print labels and submit manifests.
