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Collections are a way for you to organize kata so that you can create your own training routines. Every collection you create is public and automatically sharable with other warriors. After you have added a few kata to a collection you and others can train on the kata contained within the collection.
Get started now by creating a new collection.
Probably that you're trying to use something that the kata's Swift version doesn't allow. That or you're doing something wrong, have you googled what that error means?