Failed to find Server Action

What it means in plain English

Next.js creates non-deterministic IDs so the client can reference and call Server Actions. Those IDs can change between builds. The failed-to-find message means the ID had the expected format, but no matching Server Action was found in the current build.

That commonly happens when the client and the server are using different builds. A browser may still have assets from a previous deployment that reference a Server Action which is not present in the current deployment.

A second message, "Server Reference ID did not match the expected format," means the ID was not in the format generated by the current version of Next.js. Next.js says that can happen when the client and server run versions that use different ID formats, or when the request was intentionally malformed, including traffic from automated security scanning. If neither of those applies, Next.js says a bug may be rejecting a valid ID.

Likely causes

• The open page is still using JavaScript from the previous deployment, and the new deployment no longer has that Server Action ID.
• Self-hosted servers are not all running the same build output, or they do not share the encryption key Next.js embeds at build time.
• The client and server are on Next.js versions that do not use the same ID format, or the request was malformed.

How to fix it, step by step

1. Make the client assets and the Server Actions come from the same deployment, on compatible versions of Next.js.
2. On Vercel, use Skew Protection. Next.js says that keeps assets and Server Actions from the previous version available after a new version is deployed.
3. When you self-host across more than one server, give every instance the same build output and the same encryption key. Set process.env.NEXT_SERVER_ACTIONS_ENCRYPTION_KEY to a base64-encoded value with a valid AES key length (16, 24, or 32 bytes). Set it at build time. Next.js says the key is embedded in the build output and used automatically at runtime.
4. If the unexpected-format error keeps happening, confirm that the client and server use compatible versions of Next.js, and check whether the requests were intentionally malformed, such as automated security scanning.
5. If neither of those applies, and you can reproduce the error with a single version of Next.js, report it to the Next.js project.

How to check it worked

• The action that printed "Failed to find Server Action" runs on the deployment that served the page.
• The unexpected-format message is gone for that same action.

Sources

• https://nextjs.org/docs/messages/failed-to-find-server-action (opens in a new tab)