As to my understanding, you havent provided an authentication permission (OAuth) to the API.
Try the REST requests here
To see if it works for you.
I also think same think as Felip, It will be better to post this issue on the page of this on Branch. the person who made this QVF, will have better idea about this issue.
you could also see this video step by step to set up connection to Twitter: Connecting to Twitter using Qlik REST Connector - YouTube