Configure Mux live stream simulcast targets to fan out to multiple platforms and handle per-destination failures without interrupting the primary broadcast

Steps

1. Create a live stream and add one or more simulcast_targets, each with a destination url (rtmp(s) endpoint) and stream_key, either at live stream creation or via the create-live-stream-simulcast-target endpoint on an already-running stream
2. Check current per-plan limits on the number of simulcast targets before assuming you can fan out to an arbitrary number of platforms
3. Poll or fetch a simulcast target's status field, which starts at idle when the parent stream is disconnected and moves to broadcasting once it successfully connects to the third-party service
4. Handle the errored status by inspecting error_severity: normal means Mux will keep retrying and may recover back to broadcasting, fatal means the target is incompatible with the current input and needs reconfiguration
5. Subscribe to Mux webhooks to track simulcast target state changes in your UI instead of polling continuously
6. Confirm each downstream platform's ingest requirements (e.g., some require a broadcast/event to already be created on their side before Mux can push to the stream key)