You will need to get a goo.gl API Key to use this feature.

How to get a key

Visit the Google APIs Console, and:

  1. Create a project. You can create as many or as few projects as you need. (See the Google APIs Console FAQ for details.) Google will generate exactly one key per project.
  2. Activate the URL Shortener API. After creating a project, you should see a list of APIs, each with an Activate button. Click the one for the url shortener.
  3. Nab the key. Click "Keys" on the left-hand side to find out about yours. The "Value" is the string you want.
  4. Copy and Paste the Key in the Goo.gl API Key field and save the changes.