How to get total no. of followers of specific user? PHP

[testviiworks]

How to get total no. of followers of specific user?

I tried to used this code:
https://api.twitter.com/1.1/followers/ids.json?cursor=-1&screen_name=noradio

But this just displayed:
{“errors”:[{“message”:“Bad Authentication data”,“code”:215}]}

How to get the simplest way to get the total no. of followers using PHP only.

Thanks!