I have tried both a Get and a Post call. I still cannot figure out how to display the output of that API either through Magic Test or through the list. Do I need to add it to a database and then display it?
After a custom action to show the result you need to store it and then you can show that! If you use the Users collection in your app you can create a property and then after the custom action add a update logged in user action that adds the custom action result there. And then you can show that user property!
Or you can use a hidden input component. You can add a input component and hide it going to the edit styles and add a Change input value action after the custom action and in there select that input and for the value select the custom action result. And then you can show that input!