Standard API rate limits per app

[mp1714]

I have an app that performs actions on behalf of users through the 3-legged OAuth process. I have around 40 users that use my app.
Regarding the official Twitter docs: https://developer.twitter.com/en/docs/basics/rate-limits a user can make 400 friendships/day whereas an app can make 1000.

The problem I have is that when I reach overall 400 from all the users I receive an error. So, at the end of the day, my users can only make around 10 friendships/day, instead of 400.

Does anyone know if I'm doing something wrong?

This is how I create the users:

const user1 = new Twitter({
  consumer_key: process.env.MY_APP_CONSUMER_KEY,
  consumer_secret: process.env.MY_APP_CONSUMER_SECRET,
  access_token_key: process.env.MY_USER_ACCESS_TOKEN_KEY, (generated via OAuth)
  access_token_secret: process.env.MY_USER_ACCESS_TOKEN_SECRET (generated via OAuth)
});

Any help would be much appreciated.