This error confused me while developing with NativeScript trying to do a rest api call. Without digging thru the error object, you only get: "Response with status: 200 for URL: null" for the error text. Not exactly useful.
I then had to run "tns debug android" and dig thru the error object by doing adding a "json()" method call to it. I then got a more verbose error message. Something like:
"Error: java.net.ConnectException: failed to connect to localhost/127.0.0.1 (port 8000): connect failed: ECONNREFUSED (Connection refused)"
The chrome devtools also was cryptic only saying that the rest api call "Stalled".
Ok. So I then visited StackOverflow looking for a solution. No dice. Until, I realized that I'm doing development using an android emulator which is basically a virtual machine. And being a virtual machine calling 'localhost' or 127.0.0.1 is calling itself. The address is loopback address of the vm NOT my machine. No wonder the rest api call was failing. Fortunately, the android emulator networking is setup to work with localhost development.
The solution is to just change the rest api call from 'http://localhost/api' to http://10.0.2.2/api'.
Now it works.
For the curious, my rest api server is a Django Rest Framework app running locally.