Web API - preview_url for track is null

[anonymusdevelopment]

Country

Italy

Device

Web API

Operating System

Windows 10

My Question or Issue

I am using the Web-API for a project. I found multiple tracks, where the field "preview_url" is null in the response (nearly half of those I tested). Tried with client credentials authentication and authorization code. I get the same response, with "preview_url" set to null each time. I am wondering why I do not get null when trying the same request with the Spotify API on rapidapi.com (https://rapidapi.com/Glavier/api/spotify23/). Also setting a market where the track is available does not solve the problem.

Example track ids where this occurrs: 

• 37ZJ0p5Jm13JPevGcx4SkF
• 0QPRDC97rIQB3Jh3hrVJoH
• 1kPpge9JDLpcj15qgrPbYX
• 2tGvwE8GcFKwNdAXMnlbfl
• 4ZtFanR9U6ndgddUvNcjcG
• 5wANPM4fQCJwkGd4rN57mH
• 6uxYfENm7zw050dNUi031W

Example URL: 

https://api.spotify.com/v1/tracks?ids=37ZJ0p5Jm13JPevGcx4SkF&market=IT

Example response:

{
    "tracks": [
        {
            "album": {
                "album_type": "album",
                "artists": [
                    {
                        "external_urls": {
                            "spotify": "https://open.spotify.com/artist/58lV9VcRSjABbAbfWS6skp"
                        },
                        "href": "https://api.spotify.com/v1/artists/58lV9VcRSjABbAbfWS6skp",
                        "id": "58lV9VcRSjABbAbfWS6skp",
                        "name": "Bon Jovi",
                        "type": "artist",
                        "uri": "spotify:artist:58lV9VcRSjABbAbfWS6skp"
                    }
                ],
                "external_urls": {
                    "spotify": "https://open.spotify.com/album/0kBfgEilUFCMIQY5IOjG4t"
                },
                "href": "https://api.spotify.com/v1/albums/0kBfgEilUFCMIQY5IOjG4t",
                "id": "0kBfgEilUFCMIQY5IOjG4t",
                "images": [
                    {
                        "height": 64,
                        "url": "https://i.scdn.co/image/ab67616d000048511336b31b6a1799f0de5807ac",
                        "width": 64
                    },
                    {
                        "height": 300,
                        "url": "https://i.scdn.co/image/ab67616d00001e021336b31b6a1799f0de5807ac",
                        "width": 300
                    },
                    {
                        "height": 640,
                        "url": "https://i.scdn.co/image/ab67616d0000b2731336b31b6a1799f0de5807ac",
                        "width": 640
                    }
                ],
                "name": "Slippery When Wet",
                "release_date": "1986-08-16",
                "release_date_precision": "day",
                "total_tracks": 10,
                "type": "album",
                "uri": "spotify:album:0kBfgEilUFCMIQY5IOjG4t"
            },
            "artists": [
                {
                    "external_urls": {
                        "spotify": "https://open.spotify.com/artist/58lV9VcRSjABbAbfWS6skp"
                    },
                    "href": "https://api.spotify.com/v1/artists/58lV9VcRSjABbAbfWS6skp",
                    "id": "58lV9VcRSjABbAbfWS6skp",
                    "name": "Bon Jovi",
                    "type": "artist",
                    "uri": "spotify:artist:58lV9VcRSjABbAbfWS6skp"
                }
            ],
            "disc_number": 1,
            "duration_ms": 249293,
            "explicit": false,
            "external_ids": {
                "isrc": "USPR38619998"
            },
            "external_urls": {
                "spotify": "https://open.spotify.com/track/37ZJ0p5Jm13JPevGcx4SkF"
            },
            "href": "https://api.spotify.com/v1/tracks/37ZJ0p5Jm13JPevGcx4SkF",
            "id": "37ZJ0p5Jm13JPevGcx4SkF",
            "is_local": false,
            "is_playable": true,
            "name": "Livin' On A Prayer",
            "popularity": 84,
            "preview_url": null,
            "track_number": 3,
            "type": "track",
            "uri": "spotify:track:37ZJ0p5Jm13JPevGcx4SkF"
        }
    ]
}