ERR_VERSION_MISMATCH on Zapier: API version mismatch. Root cause: The workflow is calling a deprecated API endpoint or using a request format that is no longer supported in the current API version. Platforms regularly retire older API versions, and automations built against legacy endpoints will fail once the old version is sunset. Step 1: Identify which API version is being called. In the Zapier task history, expand the failing step and look at the "Request" details. The URL will show the API version — e.g. "/v1/", "/v2/", or "/api/2023-10/". Note this version number. Step 2: Check the platform's deprecation schedule. Go to the connected app's developer documentation and find the API changelog or deprecation notices. Confirm whether the version in the request URL has been deprecated or sunset. Most platforms give 6–12 months notice before retiring a version. Step 3: Update the Zapier app version. In Zapier, check whether the app integration itself has a newer version. Go to the Zap editor, click the app step, and look for an "Upgrade" or "Update" prompt. Zapier app versions map to API versions — upgrading the app version in the Zap will switch to the newer API endpoint automatically. Step 4: Reconnect the app after upgrading. After upgrading the Zapier app version, you will likely need to reconnect the account and re-map the action fields. The field names and data structures often change between API versions. Go through each field carefully and verify the mapping is correct for the new version. Step 5: Test with a sample record before enabling. Use the Zapier test function to run the updated step against a real sample record. Confirm the response is successful (HTTP 200) and the output data looks correct before turning the Zap back on.