How to solve the `prisma/client did not initialize yet` error on Vercel

I built an app with Next.js and Prisma, and when I tried to deploy it on Vercel I got this deployment error:

Error: @prisma/client did not initialize yet. Please run "prisma generate" and try to import it again.

The database was already initialized from my local dev install, and I just had to use it.

What did I do to solve?

I installed prisma as a dev dependency:

npm i -D prisma

and I added

"postinstall": "prisma generate"

to the scripts in package.json:

{
  "scripts": {
    "dev": "next dev",
    "build": "next build",
    "start": "next start",
    "postinstall": "prisma generate"
  },
  "dependencies": {
    //...
  },
  "devDependencies": {
    //...
    "prisma": "^2.24.1",

  }
}

That solved the problem.