Topic
HTTP callbacks one service sends to an endpoint another service operates, so events can be pushed as they happen instead of polled for.
ChatGPT has accepted MCP Events in all plans since OpenAI's DevDay on 29 September 2026, delivered only by HMAC-signed webhook. Swapping a polling tool for events means running subscription storage and callback checks against an experimental spec.
Reality
Shopify removes the subscription from a webhook whose destination is failing, and it emails the owner only when an App Store or custom app created the webhook. A merchant who builds one by hand in the admin has to watch the receiver themselves.
Reality
Developers who parse Meta's epoch-seconds webhook timestamp with new Date() get NaN and pay template rates on every WhatsApp reply, according to a dev.to post. The opposite slip, mixing milliseconds with seconds, holds the window open so free-form replies bounce silently.
Reality
A developer canceled his own subscription in production, collected two 200 webhook responses and no errors, and still saw his app promise a renewal. Stripe's stored event diff named the three fields that actually moved.
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A reconciliation job verified the charge with Paystack and marked the payment row SUCCESS, then fulfilment failed on an unrelated tenant-context bug, and the sweeper only ever reads PENDING rows.
Reality
A webhook walkthrough shows every line of a handler working correctly while the customer gets two receipts, because the sender gives up one second before the warehouse call returns and sends the event again.
Reality
A dev.to post sorts order-versus-payment disagreements into four classes. All four surface as a total that does not match, the money is already right in three of them, and only the fourth is a broken integration.
Reality
The snippet everyone pastes commits the idempotency key in one transaction and the work in another. Kill the process in between, and every later delivery hits the conflict branch and returns 200, per a dev.to walkthrough.
Reality
A dev.to design walkthrough pairs signed webhook intake with an hourly polling sweep over per-tenant API keys. It argues the architecture should be settled by what an access review can reconstruct afterwards.
Reality
A developer suspended a signed-in test user while that user's Claude agent was still running, and the app kept reading the token as valid, so enforcement has to move into a status check the application itself owns.
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One registration, one signed POST into Postgres, and a pending row for each internal reader. The design costs four row writes per event and makes acknowledgement a fact an auditor can still query a year later.
Reality
The September 11 release lets a matching finding fire a remediation action, an outbound webhook, or both. The delivery guarantees underneath it leave the receiving system to decide whether a second attempt does anything.
Reality
A dev.to design note makes a renewal reminder's business deadline the primary SLO and moves the acknowledgement behind the durable write. A 429 becomes a budget that first attempts and retries have to share.
Reality