Vercel 413 FUNCTION_PAYLOAD_TOO_LARGE

What it means in plain English

The browser sent a function more data than Vercel allows, or the function tried to send too much back. Vercel's functions limits say the maximum payload for a request body or a response body is 4.5 MB. Over that, the function returns HTTP 413 with the code FUNCTION_PAYLOAD_TOO_LARGE.

Likely causes

• A form posts a photo, a PDF, or a base64 string straight into a Route Handler or a Server Action.
• The AI generated an API route that reads await request.json() for a file the user picked.
• The function itself returns a large JSON dump or a generated file.

How to fix it, step by step

1. In the failed request, compare the body size with 4.5 MB. Vercel documents that limit on the functions limits page.
2. Stop sending the file through the function. Keep the function for a short JSON message, and put the file somewhere that accepts the upload directly.
3. If the response is the large part, do not return the whole file from the function. Return a link to the stored file instead.
4. Redeploy and retry the same upload.

How to check it worked

• The same action returns a normal status instead of 413.
• The function log no longer shows FUNCTION_PAYLOAD_TOO_LARGE.

Sources

• https://vercel.com/docs/functions/limitations (opens in a new tab)