LinkedIn API sunset version returns 426 error — no automatic fallback to supported version

Why LinkedIn returns 426 for sunset versions

LinkedIn Marketing APIs require a Linkedin-Version header in YYYYMM format. Each monthly version is supported for a fixed window; after the sunset date the server replies with HTTP 426 (Upgrade Required) instead of silently forwarding to a newer version. This behavior is documented and confirmed by the platform’s versioning policy.

Confirmed facts

• The Linkedin-Version header is mandatory for every request.
• A request with an expired version triggers a 426 response, not a redirect or silent fallback.
• LinkedIn does not provide a deprecation webhook, programmatic version discovery, or automatic upgrade mechanism.

Steps to handle the 426 error and rotate versions safely

1. Generate the header from the current UTC month: Linkedin-Version: YYYYMM where YYYY is the four‑digit year and MM is the two‑digit month.
2. Pin this version in all outbound calls until the known sunset date (typically the last day of the month).
3. Before the sunset date, automatically increment the month value (rolling over year when needed) and update the header.
4. In the request handler, catch HTTP 426. On receipt:
   1. Log the event with the offending version.
   2. Retry the same request using the next month’s version (incremented header).
   3. Apply exponential back‑off and limit retries (e.g., max 3 attempts) to avoid traffic spikes.
   4. If the retry also fails with 426, raise an alert for manual investigation.
5. Unit‑test the retry logic by mocking a 426 response and asserting that the client retries with the incremented header.
6. Monitor production logs for 426 occurrences; verify they line up with the published sunset calendar and that the automated retry succeeds within the back‑off window.

Missing diagnostic detail that could change the recommendation

Do you have a reliable source of current UTC time within your integration (e.g., a synchronized clock or an external time service)? If the system clock may drift, the generated Linkedin-Version could be incorrect, causing unnecessary 426 errors. In that case, replace local time with a trusted time API before generating the header.