With the Rules Engine, you can create rules to allocate different couriers based on your custom Package Types.
To demonstrate how to do this, in our example we'll show you how to ensure a custom 'Large Box' is allocated to Allied Express.
If you haven't set up your Custom Preset yet, navigate to your Pick & Page page in your Settings to do this. Here's what we've created below.
Ensure that your preferred courier is switched on in your Carrier Settings. For this example, it would be Allied Express.
When creating a rule, select Package Type from the dropdown list of conditions. Next, select Contains from the next dropdown and enter 'Large Box'.
In the next section, enter all the couriers that you do not want the 'Large Box' packaging type allocated to.
Click on save and ensure you've switched the rule ON.