Why am I getting referrer undefined?

That's because, the production API will not let you through if your referrer header is not defined properly. So if you are using this api on your website to get your instagram posts, then it would work just fine, because the browser will automatically add the required headers.

Q: But, I need this to scrape IG? A: Fork the API and switch the undefined referer check off here

Q: I am still getting undefined, is the API down? A: My blog uses the API to display my IG feed, if you see it running on https://nishantarora.in it is not down.

Q: I just want to see the output of the api. A: Try clicking here

Raise an issue if something is not clear.