Errors in Custom Actions and Zapier MCP requests due to duplicated query parameters

What to do

• Check whether your product depends on Zapier. Check your stack

  Paste a package.json, lockfile, Terraform or a list of domains at down.guide/stack to see every provider you depend on.

• Confirm your retries, queues and scheduled jobs caught up after the 1h 48m it lasted.

  Anything that failed between 2026-10-12 08:39 UTC and 2026-10-12 10:27 UTC may need a replay.

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Updates from Zapier 3

1. identifiedOct 12, 2026, 8:39 AM UTC

   We've identified an issue where some requests made through Custom Actions in Zaps or Zapier MCP include duplicated query parameters. Because of this, some customers may see errors even when their inputs are valid. Not every app or request is affected, since many apps handle duplicate query parameters without issue. Standard app actions for connected apps that run in Zaps are not affected. We'll update this page as soon as we have more information. If you need help, please reach out to our Support team at [https://zapier.com/app/get-help](https://zapier.com/app/get-help "https://zapier.com/app/get-help").

   provider

2. monitoringOct 12, 2026, 10:12 AM UTC

   A fix has been deployed that stops Custom Actions and Zapier MCP requests from sending duplicated query parameters. Error rates on affected requests dropped to normal immediately after deployment (~09:40 UTC). Not every request failed during the issue, and we have not identified evidence of data loss. If a connected app behaved unexpectedly during this window, please reach out so we can take a closer look. We’re continuing to monitor and will post a final update within 24 hours. If you need help, please reach out to our Support team at [https://zapier.com/app/get-help](https://zapier.com/app/get-help "https://zapier.com/app/get-help").

   provider

3. resolvedOct 12, 2026, 10:27 AM UTC

   The issue causing duplicated query parameters on some Custom Actions and Zapier MCP requests has been resolved. Starting October 7, a deploy caused some outbound requests to include duplicate query parameters, which a subset of connected apps rejected even when inputs were valid. Not every request was affected, and standard app actions in Zaps were not impacted. A fix was deployed on October 12 at 09:40 UTC to remove the duplicated parameters, and error rates returned to normal immediately. We’ve been monitoring since and have not identified any further impact or evidence of data loss. We’re reviewing the change that introduced this to prevent similar issues going forward. If you experienced errors during this window and still need help, please reach out to our Support team at [https://zapier.com/app/get-help](https://zapier.com/app/get-help "https://zapier.com/app/get-help").

   provider

Corrections

None so far.

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