A "routes-manifest.json" couldn't be found - next.js

Question

I'm following this tutorial so that I generate a static file during the vercel build. I've tried moving the files around but it always shows a log like:
23:41:48.432 $ node ./pages/api/build.js 23:41:48.493 Build time file created successfully! 23:41:48.495 Done in 0.09s. 23:41:48.507 Error: A "routes-manifest.json" couldn't be found. This is normally caused by a misconfiguration in your project.
Then it links to this. I've checked the issues and everything seems to be fine.
If I remove the "vercel-build": "node ./pages/api/build.js" line from package.json, the error disappears. But also the functionality..
my pages/api/index.js file:
const BuiltTime = require('./built-time');
module.exports = (req, res) => {
res.setHeader('content-type', 'text/plain');
res.send(`
This Serverless Function was built at ${new Date(BuiltTime)}.
The current time is ${new Date()}
`);
};
my pages/build.js:
const fs = require('fs');
fs.writeFile(
'pages/api/built-time.js',
`module.exports = '${new Date()}'`,
(err) => {
if (err) throw err;
console.log('Build time file created successfully!');
}
);
my package.json:
{
...
"scripts":{
"vercel-build": "node ./pages/api/build.js",
}
}

Answer 1

In the end I didn't use "vercel-build". I just run a script before the build:
// package.json
{
"scripts": {
"make-q": "node ./build.js",
"build": "yarn run make-q && next build",
}
The build file can't use import or call typescript files (at least for now):
// build.js
const slugify = require('./utils/slugify');
const fs = require('fs');
const qs = slugify('some string');
fs.writeFile(
'questionsDB.js',
`module.exports = ${JSON.stringify(qs, null, 2)}`,
(err) => {
if (err) throw err;
console.log('file created successfully!');
}
);
Finally, inside the pages/api/test.js:
const db = require('../../db');
module.exports = (req, res) => {
res.setHeader('content-type', 'text/plain');
res.send(`
working:
${db}
`);
};
Now, if I call url/api/test I get the result based on the build.
Things I tried that failed:
Different node version
Update nextjs
remove yarn.lock and build again