Embed API does not run locally

I'm trying to play with embedding a pdf, but it does not work. In the manual it says that credentials are not required when running locally (I have local Django server at http://127.0.0.1:8000/)  but it does not seem to be the case. I tried to obtain ID for local address, but this seems to be impossible too. My project is not hosted yet, so I can't try getting credentials for a domain.