This error occurs when you deploy your Express application to Vercel without a build folder, say you don't have a frontend, and you still wanna deploy your project, then just follow the Steps it will work fine.

1. Go to Vercel -> project -> Setting -> Build and Output Settings then set Output Directory to . ( a dot meaning project root )

2. If you are using Multer and Cloudinary for Images, then might you need to change your public/temp into just '/tmp' in your Multer configuration.

These two Steps helped, I hope if someone encounters the same error, it will help.

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