401 Unauthorized Error During Vercel Build with Sanity

I understand you're getting a 401 Unauthorized error during your Vercel build! This is a common authentication issue with Sanity projects. While you mentioned the full error message is in the thread below, I can help you troubleshoot the most likely causes.

A 401 error typically means Sanity can't authenticate your request, usually due to missing or incorrect API tokens. Here are the most common culprits:

Check Your Environment Variables

The most frequent cause is missing or incorrectly configured API tokens in your Vercel environment variables:

1. Verify the token exists in Vercel: Go to your Vercel project settings → Environment Variables. Make sure you have your Sanity token set (commonly named SANITY_API_TOKEN, SANITY_API_READ_TOKEN, or NEXT_PUBLIC_SANITY_TOKEN depending on your setup).

2. Check which environments it's enabled for: Ensure the token is enabled for "Production" (and "Preview" if needed), not just "Development".

3. Redeploy after adding variables: If you just added the environment variable, you need to trigger a new deployment for it to take effect.

Generate the Correct Token

If you need to create or verify your token:

1. Run npx sanity@latest manage from your project directory, or access Manage from your Studio menu

2. Navigate to the API tab

3. Create a new token with appropriate permissions:

   • For read-only access (most frontend builds): use Viewer permissions
   • For preview/draft content: you'll need at least Viewer permissions on the appropriate dataset

4. Copy the token and add it to your Vercel environment variables

Common Token Issues

• Using a personal token instead of a robot token: For production builds, use robot tokens rather than personal tokens
• Token doesn't have access to the dataset: Make sure the token has permissions for the dataset you're querying (usually production)
• Accessing draft content without authentication: If you're using perspectives like previewDrafts or querying draft documents, you must include a valid token
• Token stored incorrectly: Store tokens in environment variables, never hardcode them in your code

Variable Naming

Double-check that your code is looking for the same environment variable name you've set in Vercel. If your code expects SANITY_API_READ_TOKEN but Vercel has SANITY_API_TOKEN, they won't match.

If you can share the specific error message or relevant parts of your build logs, I (or others in the community) can provide more targeted help! Look especially for lines mentioning "401", "unauthorized", or "authentication".