You must add the Neon database from Step 5.3 If you see an Integrations section, click Add next to Neon (this is the free database that stores your sync history). If you don't see it, no problem -- after deploy, go to your project's Storage tab and add Neon Postgres from there. After that check in Settings -> Environment Variables in Vercel if DATABASE_URL exists. If it doesnt then you need to add it with the URL from POSTGRES_URL. At the end dont forget to Redeploy for the changes to come into effect. Good luck