Okay I've solved it: Its important to convert the string to an NSString. The dictionary would become this: let metadata : NSDictionary = [ HKMetadataKeySyncIdentifier : NSString(string: match.syncIdentifier.uuidString), HKMetadataKeySyncVersion: match.syncVersion ] I'm leaving it up here in case somebody else comes across the same problem

Same here, I can't implement it on watchOS 7.3

It works on device for me! (Sorry, can't edit my old post anymore)

Hi, Yeah it seems to be pretty buggy. For example, animations don’t work and .onChange does not get called. I solved it by using .overlay and manually position the view.