mockoon | quickest way to run mock APIs | REST library

I am using mockoon for API simulation. I created 2 routes there with method GET and its body contains(responds with) JSON object. I noticed that my express app is not able to parse one of the routes. But the route that has JSON object in body which contains ARRAY is getting parsed. I tested both routes with Express(by console.log) and in chrome browser(I have JSON formatter extension) and it is behaving the same meaning response that does not contain ARRAY is not getting parsed but the response with array is getting parsed(behaving normally). Let me show the screenshots:
Express(by console.log):
With array:
Without array:

Chrome(JSON Formatter extension):
With array(extension is able to parse):
Without array(extension is not able to parse):

I tried adding Header(Content-Type: application/json) to the route in mockoon. But still, I am not aware of what is going on here. Someone please explain

The express code: