Ember : Could not find module `@ember-intl/intl-relativeformat` imported from `ember-intl/services/intl`

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