Integration Fields are still in beta and will be progressively deployed to all repositories. This feature allows you to connect your prismic.io repository to an external API. If you don't already have Integration Fields in your repository, don't hesitate to ask for it in the chat support or slack community.
After creating your Integration Field
This article assumes that you have already set up an Integration Field in your prismic repository settings. If you want to know more about Integration Fields in general, you can learn the basics of Integration Fields.
After setting up an Integration Field in your settings, the next step will be to add this to your custom type.
Add your new Integration Field to your Type
As soon as you've configured the Integration Field you will be able to add your Integration Field to your Custom Types (even before it's finished synchronizing).
Simply go to the edit page for the Custom type you wish to add it to. You will find your Integration Field at the bottom of the content field list.
Like any other field, you will be able to drag & drop the Integration Field directly where you want it in your Custom Type. You can add it in a Group, a Slice, or as a regular field.
Save your Custom Type and you're good to go! You will now see this field in the editor for this Custom Type, and the content editors will be able to select products from your catalog or custom API.
All that is left is to learn more about selecting an Item in the editor.