First you need to create a calendar subscription.
Be sure to select a file format under the Calendar tab.
If you have a Pro Account, you can download most calendars in various formats through the API. This is intended for users who use to utilize the data in applications, websites and such.
Please note that API access is not available for the following calendars: Pokémon Go Events, Rocket launches, Tides, UV index, Weather, Premiere movies, Baseball, Basketball, Formula 1, Football, Ice-Hockey, Soccer, Tennis, WRC, National elections, Pregnancy.
First you need to create a calendar subscription.
Be sure to select a file format under the Calendar tab.