If you're having trouble deploying an Express app, this guide can help.

https://vercel.com/guides/using-express-with-vercel

You can also ask v0 for suggestions tailored to your own project setup.

Hey @gyanendra-7337!

Thanks for joining us here from X, glad we’ve got more context now 😊

Looks like this error’s happening because your project is mixing CommonJS and ES modules. The jose package is ESM-only, but @better-auth/core is trying to import it using CommonJS (require()), which causes the issue.

Here’s what you can try...

1. Convert your project to ES modules (recommended)

• Add "type": "module" to your package.json
• Replace all require() calls with import
• Make sure to include .js extensions in your imports

This is the cleanest long-term fix and should solve the compatibility issue entirely.

2. Check your better-auth setup

• Make sure you’re on the latest version of better-auth
• Check if they have Vercel deployment notes or examples

3. Set your Node.js runtime on Vercel

If you’re using serverless functions, you can explicitly set the runtime:

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{
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  "functions": {
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    "app.js": {
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      "runtime": "nodejs18.x"
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    }
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  }
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}

If you’re on Next.js with the App Router, try using an Edge Function or Server Action, which support ES modules out of the box.

@pawlean Thanks for this, crazy support from you. Thanks a lot

Do you have any idea what tsconfig properties we need to set to add file extensions on build?

Glad I could be of help! What I'm here for

Try updating your tsconfig.json like this:

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{
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  "compilerOptions": {
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    "target": "ES2022",
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    "module": "ESNext",
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    "moduleResolution": "Bundler",
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    "esModuleInterop": true,
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    "resolveJsonModule": true,
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    "skipLibCheck": true,
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    "outDir": "dist"
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  }
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}

Then either:

• Manually include .js in your imports (e.g. import { x } from './utils.js'), or
• Run a tool like tsc-esm-fix after tsc to automatically add file extensions.

TypeScript itself won’t rewrite the paths, so tsc-esm-fix is the simplest way to make your ESM output work cleanly on Vercel.

Hi @gyanendra-7337! 🙂

We haven't heard back from you. If you're still stuck, feel free to share any updates, logs, or additional context that might help us assist you better!