Create navigation item using REST API with non-existing link in SharePoint Online

I've stumbled upon issue where I need to create a link in navigation from root site which points to site collections.

POST Request URL: https://contoso.sharepoint.com/_api/web/navigation/TopNavigationBar

Body:

{
    "__metadata": {
        "type": "SP.NavigationNode"
    },
    "Url": "https://contoso.sharepoint.com/sites/nonexisting",
    "Title": "Non existing"
}

Error response:

{
    "odata.error": {
        "code": "-2130247147, Microsoft.SharePoint.SPException",
        "message": {
            "lang": "en-US",
            "value": "Cannot open \"/sites/nonexisting\": no such file or folder."
        }
    }
}

Tried to create it manually - works fine. Got new link by REST API to check properties:

{
                "AudienceIds": null,
                "CurrentLCID": 1033,
                "Id": 7617,
                "IsDocLib": true,
                "IsExternal": true,
                "IsVisible": true,
                "ListTemplateType": 0,
                "Title": "Nonexisting",
                "Url": "/sites/nonexisting"
}

Nothing out of ordinary.

I'm wondering, is it even possible to create such links with REST API?