Player controls on ios lock screen don't show up

Question

I would like to show play/pause controls on the ios lockscren. It's an audio app using libPd. What I did so far :

In the Info.plist : Set the value of the key "Required background modes" to "App plays audio or streams audio/video using AirPlay"

In the capabilities : Enable Background Modes ("Audio, Airplay, and Picture in Picture")

In the source code :

Configure the AVAudioSession :

try! AVAudioSession.sharedInstance().setCategory(AVAudioSessionCategoryPlayback, with: [])

try! AVAudioSession.sharedInstance().setActive(true)

add infos to the MPNowPlayingInfoCenter :

let nowPlayingInfo = [
        MPMediaItemPropertyArtist: "test",
        MPNowPlayingInfoPropertyPlaybackRate: NSNumber(value: 1.0 as Float)] as [String : Any]

MPNowPlayingInfoCenter.default().nowPlayingInfo = nowPlayingInfo

Nothing appear on the lockscreen/control center. I don't understand what triggers the control display. When I use a AVAudioPlayer and play it, it works. But I guess those controls are not limited to AVAudioPlayer.