Different issue: I am trying to build against Ktor darwin-legacy, since I need to support iOS 12, but the iOS app launch still fails with the Symbol not found: _OBJC_CLASS_$_NSURLSessionWebSocketMessage error. I am setting darwin-legacy in the darwinMain sourceSet, and the client-core, serialization-kotlinx-json and client-content-negotiation in commonMain. Could these items in common be pulling in the non-legacy darwin versions?