Ember : Could not find module `#ember-intl/intl-relativeformat` imported from `ember-intl/services/intl` - ember.js

Question

I added the module ember-intl in my app since the ember-i18n is deprecated.
so yarn works well, updates package.json and yarn.lock (i got rid of the package.lock),
but i get this error on the browser's console after a successful ember build:
Error: Could not find module #ember-intl/intl-relativeformat
imported from ember-intl/services/intl
But in my node_modules the folders #ember-intl/intl-relativeformat and ember-intl both exist.
in the yarn.lock i have this line:
"#ember-intl/intl-relativeformat#^2.1.0":
more info:
Ember : 3.5.1
Ember Data : 3.5.0
jQuery : 3.3.1
Ember Remodal : 2.18.0

Answer 1

I solved this problem by adding ember-auto-import to my project. It comes pre-installed in new Ember projects, but needs to be added manually to older ones.
Just run ember install ember-auto-import and that's it.

Answer 2

I just installed it to see if a blank slate would show me that error.
It did not. : /
I just had a few beers... but I just want to make sure you imported the service.
the docs show:
// app/routes/application.js
export default Route.extend({
intl: service(),
beforeModel() {
return this.intl.setLocale(['fr-fr', 'en-us']); /* array optional */
}
});
but like most docs - assume you know the larger ecosystem. It's a tiny possibility that you might not have imported the module above import Service from '#ember/service'; etc.? https://guides.emberjs.com/release/applications/services/
if not that... then track down the mentioned 'ember-intl/services/intl' and see if you can figure out why the '#ember-intl/intl-relativeformat' import isn't jiving. Maybe check the repo and the version - and ask there on GitHub?
Good luck!