To connect a Checkout configuration to Kustom Checkout using the Checkout API, you need a connection ID and a Kustom Secret. The Kustom Secret can be created for any connection. Follow the instructions below:

1. Log into nShift Portal, select Checkout, and go to Connections in the top menu. Here you will see a list of all your connections including the connection ID associated with each connection. 
   
   
2. Click on the connection for the Checkout configuration you want to connect to Kustom Checkout.
   
   
3. Click Create Kustom Secret.
   
   
   
   
4. The Kustom Secret will now be displayed on the screen. It is important to copy the code before clicking Continue as you will not be able to view it again after closing the dialog. 
   
   
5. Add the Kustom Secret and the Connection ID to your Shipping Profile in the Kustom Merchant Portal. Choose "nShift" as the TMS. If you need support on how to configure your profile in the Kustom Merchant Portal, please reach out to Kustom or contact them via email: support@kustom.co . 

If you want to create a new connection to use with your Kustom integration, you can find more detailed instructions in this article: Managing Connections

For more information on the Checkout API, read this article: Getting started with nShift Checkout API