ERR_429_ZAPIER on Zapier: Zapier Task Loop Triggers Repeated 429 Rate Limit Errors. Root cause: A Zap triggers itself recursively — typically when an action writes back to the same app that fires the trigger — causing Zapier to hammer the downstream API until the platform enforces a 429 rate-limit block. The loop continues until the Zap is manually paused or the account task limit is exhausted. Step 1: Identify the Recursive Trigger. Open the Zap history and look for back-to-back identical trigger events within seconds of each other. The trigger app and the action app will be the same, or the action will modify a field that the trigger watches. Step 2: Add a Loop-Break Filter. Insert a Filter step immediately after the trigger. Add a condition such as "only continue if [modified_by] does not contain Zapier" or "only continue if [source] is not automation". This prevents the Zap from processing records it created itself. Step 3: Implement Delay or Deduplication. Add a Delay by Zapier step of 2–5 minutes between trigger and action. For high-volume Zaps, use a Formatter step to hash the record ID and store it in a Zapier Storage key to detect and skip already-processed records. Step 4: Set API Rate Limit Awareness. Check the downstream API documentation for its rate limit (requests per minute/hour). In Zapier, use the built-in throttle settings or split high-volume Zaps across multiple accounts to stay within limits.