It also doesn’t work for me. What does work is using API key.
Get your key here: https://www.beeminder.com/api/v1/auth_token.json
And configure your goal like this:
Also replace drinks-water with whatever your goal name is.
https://www.beeminder.com/api/v1/users/USERNAME/goals/GOALNAME/datapoints.json?auth_token=KEY