How can I fetch the complete main navigation menu via JSON:API? How can I fetch the complete main navigation menu via jsonapi?

I've tried:

curl --header 'Accept: application/vnd.api+json' https://cms.example.com/jsonapi/menu/menu/


and

 curl --header 'Accept: application/vnd.api+json' https://cms.example.com/jsonapi/menu/menu/232fc942-51f3-4478-8535-e5dc482a166e


where 232fc942-51f3-4478-8535-e5dc482a166e is the id of the main-navigation menu BUT only the first level nodes are returned:

{
  "data": {
    "type": "menu--menu",
    "id": "232fc942-51f3-4478-8535-e5dc482a166e",
    "attributes": {
      "label": "Main navigation"
    },
    "links": {
      "self": {
    "href": "https://cms.garanteasy.com/jsonapi/menu/menu/232fc942-51f3-4478-8535-e5dc482a166e"
      }
    }
  },
  "jsonapi": {
    "version": "1.0",
    "meta": {
      "links": {
    "self": {
      "href": "http://jsonapi.org/format/1.0/"
    }
      }
    }
  },
  "links": {
    "self": {
      "href": "https://cms.garanteasy.com/jsonapi/menu/menu/232fc942-51f3-4478-8535-e5dc482a166e"
    }
  }
}
I did not get it to run with JSON:API, there are several long-standing issues...

However you can get it to run if you additionally install the REST Menu Tree module.

Be aware that this has several direct and indirect dependencies:

It has a direct dependency on Menu Normalizer and according to this issue you need to then activate that endpoint for example with the REST UI module - which in turn will activate the core REST module.

Then in your site activate the endpoint via the Rest UI in /admin/config/services/rest.

Afterwards you might also want to allow everyone to GET this endpoint via /admin/people/permissions#module-rest

And finally you get a JSON array in /entity/menu/main/tree.
Or query a different menu via /entity/menu/{internal_menu_name}/tree.