There's another community post with 404 debugging tips that might be helpful. Please give these solutions a try and let us know how it goes.

https://community.vercel.com/t/debugging-404-errors/437

Vercel Community

Debugging 404 Errors

Sometimes things don’t go as expected when deploying a website. If you see a 404 on your site, that means the page or resource couldn’t be found. There are...

A human should be around soon to offer more advice. But you can also get helpful information quickly by asking v0.

Hi Checkpc2012,

First, I’d edit the post and remove the project ID, deployment IDs, team name, and commit hash. They are not API keys, but they are still internal project/account identifiers that usually do not need to be public.

For the issue itself, the useful distinction is:

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Generated deployment URL -> 401 because Deployment Protection is enabled
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Stable production alias   -> 404 NOT_FOUND at Vercel edge
3

That does make it look more like alias/routing state than a Next.js route problem, especially if the app build completed and the deployment is Ready.

I’d run these from the same Vercel scope:

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vercel switch
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vercel alias ls --limit 100
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vercel inspect dpl_2B8FZLfK1UXNASiY8JjnpfHXcJGR
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Then check whether 3t-app-staging.vercel.app appears exactly once and points to the current deployment. If there are old/stale aliases for the same project, remove the stale one and assign the alias again:

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vercel alias rm 3t-app-staging.vercel.app
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vercel alias set dpl_2B8FZLfK1UXNASiY8JjnpfHXcJGR 3t-app-staging.vercel.app
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If the CLI already shows the alias correctly assigned after re-setting it, but the public URL still returns:

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X-Vercel-Error: NOT_FOUND
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then I don’t think more app-code debugging will help much. At that point the useful public evidence is just:

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Alias: 3t-app-staging.vercel.app
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Deployment state: Ready
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Alias shown on deployment: yes
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Public alias response: 404 NOT_FOUND
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Latest X-Vercel-Id: gru1::82srb-1781564125375-b149eb9c7ef8
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Timestamp: 2026-06-15T22:55:24Z
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Generated deployment URL returns 401 due to Deployment Protection
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That should be enough for Vercel to check whether the alias exists in the control plane but has not propagated correctly to the edge routing layer.