Google Calendar only supports calendar URLs up to a maximum of 250 characters. If your calendar feed url is longer than this, you will need to use a url shorten in order to get it to load into the calender.

In order to shorten a calendar feed url:
  1. Copy the URL of your calendar feed
  2. Go to https://goo.gl/ 
  3. Paste the URL of your calendar in the box
  4. Remove the webcal:// section from the beginning of the url
  5. Click Shorten URL
  6. Copy the generated short URL
  7. Use the shortened url to add the calendar into Google Calendar