Without knowing more about the API, my guess is that you need a list of objects rather than a list of nested objects.
Can you provide a link to the API documentation?
What is the value of app variable name? You can display it in a text input and then copy and paste it into a post here. You may want to hide the authentication values in it.
If you use that value in a third-party client such as Postman, are you able to get a successful response from the API?
If not, how have you accessed the API outside of Thunkable? That’s a useful first step before trying to build the blocks to make it work in Thunkable.