moment(...).tz is not a function
If you're using Node.js, you may accidentally be using
const moment = require('moment'); //moment
instead of
const moment = require('moment-timezone'); //moment-timezone
Also, make sure you have installed moment-timezone with
npm install moment-timezone --save
Explanation
The bug of requiring moment without timezones could occur by installing moment
with require('moment'), later deciding to npm install moment-timezone, and then
forgetting to update the require.