Update 10th March 2023: Strava has increased Intervals.icu rate limits. All Intervals.icu users will continue to be able to download activities from Strava. More info here: Strava sync available to all users!
Intervals.icu has exhausted it’s Strava API rate limit every day for the last week and Strava are no longer increasing rate limits. This means that I have to make downloading activities from Strava a premium feature to reduce the number of calls to the Strava API. This will happen later this week. Future new users and current free users will be able download from Strava for a few weeks after which time a subscription will be required.
Downloading activities from Garmin, Polar, Suunto, Wahoo and Dropbox does not require a subscription.