Hello.
I added custom “missing environment variables” error pages for both frontend and backend for FastAPI Next.js starter project. I tested monorepo deployment using a single “Vercel Deploy” button and it works correctly. After initial deploy a developer just needs to add environment variables and migrate and seed Neon database using local development environment. I documented deployment process in detail, the links are bellow.
Also I wrote “Template page draft” MD file that you can reuse or customize.
For the Astro developer blog project I inferred SITE_URL from VERCEL_PROJECT_PRODUCTION_URL and made Plausible env vars optional. In this way the developer just needs to click “Vercel Deploy” button and will have a fully running app with zero env vars and integrations to configure. I tested this and it works correctly.
I also wrote “Template page draft” MD that you can reuse. Also added documentation how to deploy using both “Vercel Deploy” button and Github Actions.
I apologize for a lot of links, it can look overwhelming. Please let me know if you need any additional help.
FastAPI Next.js starter
Custom “missing environment variables” error pages:
Frontend:
Backend:
Template page draft: https://github.com/nemanjam/full-stack-fastapi-template-nextjs/blob/main/docs/vercel-template.md
Vercel button code: https://github.com/nemanjam/full-stack-fastapi-template-nextjs/blob/vercel-deploy/docs/notes/vercel/vercel-button-monorepo.md
Deploy to Vercel link: 
Deploy to Vercel documentation:
Backend docs: https://github.com/nemanjam/full-stack-fastapi-template-nextjs/tree/main/docs/vercel-deployment-backend.md
Frontend docs: https://github.com/nemanjam/full-stack-fastapi-template-nextjs/tree/main/docs/vercel-deployment-frontend.md
envLink and envDescription params for Vercel Button:
# Backend
envDescription=https://github.com/nemanjam/full-stack-fastapi-template-nextjs/tree/main/docs/vercel-deployment-backend.md#environment-variables
envLink=https://github.com/nemanjam/full-stack-fastapi-template-nextjs/blob/vercel-deploy/.env.vercel.example
# Frontend
envDescription=https://github.com/nemanjam/full-stack-fastapi-template-nextjs/tree/main/docs/vercel-deployment-frontend.md#environment-variables
envLink=https://github.com/nemanjam/full-stack-fastapi-template-nextjs/blob/vercel-deploy/frontend/apps/web/.env.vercel.example
Astro developer blog
Template page draft: https://github.com/nemanjam/nemanjam.github.io/blob/main/docs/working-notes/vercel/vercel-template.md
Vercel button code: https://github.com/nemanjam/nemanjam.github.io/blob/main/docs/working-notes/vercel/vercel-button.md
Deploy to Vercel link: 
Deploy to Vercel documentation: https://github.com/nemanjam/nemanjam.github.io/tree/main#3-vercel
envLink and envDescription params for Vercel Button:
envDescription=https://github.com/nemanjam/nemanjam.github.io#environment-variables
envLink=https://github.com/nemanjam/nemanjam.github.io/blob/main/.env.production.example