Google Calendar only supports calendar URLs up to a maximum of 250 characters. If the calendar feed URL is longer than 250 characters, users will need to use a URL shortener in order to get it to load into the calendar.

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