Troubleshooting Claude Code and Knack

What you'll learn

Most problems with a Claude Code frontend show up at sign-in, even when the real cause is somewhere else entirely. This article covers the errors specific to hosting your own frontend, what each one actually means, and how to fix it.

Sign-in fails with redirect_uri_mismatch

What you see: An error naming an address, such as Redirect URI not registered: http://localhost:5173/auth/callback.

What's happening: Knack only returns users to addresses registered in advance. The address your app sent is not on the registered list. The difference is often small, such as http where https was registered.

How to fix it: Make the two match. Ask Claude Code to register the address your app is actually running on. Knack requires https, so a plain http address cannot be registered at all, including on localhost.

The deploy fails and mentions a missing configuration file

What you see: The build finishes, then the deploy step fails. The log mentions a missing configuration file or entry point. Nothing gets published.

What's happening: Your host's deploy command expects a configuration file in your project telling it what to publish. Claude Code adds that file when it knows where you are deploying. If your host was never mentioned, the file is not there.

How to fix it: Tell Claude Code which host you are deploying to and ask it to add the configuration that host needs. Then push the change and deploy again.

How to prevent it: Mention your host in your first description of the app. One sentence saying where the app will live is enough.

The deploy succeeds but the address loads nothing

What you see: The deploy reports success with no errors. The web address returns nothing, or you cannot find the address at all.

What's happening: Your app is published, but its public web address is switched off. Some hosts disable it by default and do not mention it during setup.

How to fix it: Look for a domains or settings screen in your host's dashboard and enable the production address.

The home page works but sign-in returns a 404

What you see: Your deployed app loads correctly. Sign-in then fails, or the page you return to after signing in shows a "not found" error.

What's happening: Most custom frontends deliver a single file, and the app draws each screen after that. The address Knack returns users to is not a file on your host, so the host looks for it, finds nothing, and returns a 404 before your app can load and handle it.

How to fix it: Your host needs to be told to serve your app for any address it cannot find. Ask Claude Code to configure that for your host.

This one is worth recognizing by shape. The error appears at sign-in, so it looks like an authentication problem. It is a hosting setting, and no amount of checking your Knack configuration will find it.

Everyone gets signed out after you change the app's address

What you see: Sign-in worked, then stopped for everyone at once, shortly after you moved the app to a new address or added a custom domain.

What's happening: Changing your app's address requires registering the new one with Knack. Re-registering ends active sessions.

How to fix it: Register the new address, then ask users to sign in again. Expect this whenever the address changes, and plan address changes before you invite real users.

Sign-in works but the user sees no records

What you see: A user signs in successfully and lands on an empty screen. No error appears.

What's happening: This is not a hosting problem. Sign-in worked, so the connection is fine. The user is being shown nothing because of how record access is configured or how your frontend is asking for records.

How to fix it: Start with Checking That Your Access Rules Actually Work. An empty screen with no error is almost always access control behaving as configured, rather than a bug in your app.

Next steps

• Hosting a Claude Code Frontend for Knack covers the setup these errors come from.
• Connecting Claude Code to Knack covers the Knack MCP Server connection.
• Troubleshooting Your Knack Connection covers problems that apply to any custom frontend, not only Claude Code.