The HighLevel API is capable and, in places, opinionated. Most integration pain we get called into comes from four sharp edges that are all avoidable if you know they exist. This is the guide we wish every developer read before their first build against the platform.
Webhooks: assume at-least-once, sometimes never
Design for duplicate deliveries with idempotency keys on your side, and design for missed deliveries with a reconciliation sweep that polls for changes on a schedule. Webhooks are a fast path, not a source of truth.
Log every payload raw before processing. When a client asks why something did not sync three weeks ago, that log is the difference between an answer and a shrug.
Rate limits and burst behavior
Bulk operations that work in testing fail in production when a client has 80,000 contacts. Respect the documented limits, back off exponentially on 429s and queue writes rather than firing them in loops.
The pattern that survives: a worker queue with per-location concurrency caps. The pattern that pages you at 2am: a for-loop over contacts with an API call inside.
Versioning and token hygiene
Pin your API version explicitly and read the changelog monthly. Refresh tokens before they expire, store them per location and handle the revoked-token case gracefully - agencies uninstall and reinstall apps more often than you think.
Treat a 401 as a state to recover from, not an error to alert on. Your app should re-auth and resume without a human involved.
Key takeaways
- Webhooks are at-least-once: dedupe on your side, reconcile on a schedule
- Queue writes with per-location concurrency caps - never loop raw API calls
- Pin API versions, refresh tokens early, recover from 401s automatically
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