My customer does not see BorderGuru as a shipping option at checkout

Most of the time, this type of issue can be resolved with a simple configuration update. 

Is BorderGuru configured as a shipping method for the customer’s region?

For a customer to use BorderGuru, your Shopify store must be configured to show BorderGuru as an available shipping option for their region. You can verify this by going to your Shopify admin panel and navigating to:

Settings → Shipping and Delivery → General Shipping Rates

In this menu, you'll see a section called Shipping Zones. Make sure that the country your customer is ordering from has BorderGuru listed as a shipping method.

For example, in the screenshot below, the shipping zone labeled "Rest of World" includes BorderGuru as a configured shipping method.