As far as I can tell, that App ID should be approved for Ads API already.
As an idea did you update the default profile that twurl is using?
Try typing “twurl accounts” and then "twurl set default ". The details of how twurl is doing authentication are stored in the .twurlrc file.
Which OS are you running twurl from? Is it 0.9.3 when you type twurl --version?
You might also try hitting the production endpoint instead of Sandbox to see if it makes a difference. Another option would be to use the Ruby or Python SDK which are not so difficult to set up, but it shouldn’t be much different and I would expect you to be able to get twurl working.