If you can't get MyPost Business services to show for your orders, there are a few things to check in our app.
Make sure you have enabled all of the services that you would ship with in the CARRIER settings for MyPost. See our help article for how to do that here.
Then in SHIPPING RULES, ensure for the "Default Carrier/Service" section you have enabled more than one service. Enable all the services you would normally ship with (all sizes of Parcel Post and Express) - our system will automatically assign the cheapest.
eg:
The same goes for the shipping rules you have created.
If you select multiple options, our system will choose the cheapest one if a rule matches, eg:
