Amazon Prime Music addon not working with flatpak version of Kodi.
As it seems the problem is related to FFMPEG.
The problem is not present in the kodi from rpmfusion.
Flatpak -> ffmpeg-4.0.3-Leia-Beta5.tar.gz
rpmfusion -> ffmpeg-4.0.2-Leia-Alpha3.tar.gz
Please see the debug log below:
19:49:06.320 T:140421724362496 DEBUG: https://music.amazon.de/dmls/
19:49:06.430 T:140422785566720 DEBUG: ------ Window Init (DialogBusy.xml) ------
19:49:06.756 T:140421724362496 INFO: CPythonInvoker(7, /home/afrase/.var/app/tv.kodi.Kodi/data/addons/plugin.audio.prime_music/default.py): script successfully run
19:49:06.756 T:140421724362496 DEBUG: onExecutionDone(7, /home/afrase/.var/app/tv.kodi.Kodi/data/addons/plugin.audio.prime_music/default.py)
19:49:06.772 T:140422785566720 DEBUG: ------ Window Deinit (DialogBusy.xml) ------
19:49:06.772 T:140421732755200 DEBUG: Thread scriptobs 140421732755200 terminating
19:49:06.772 T:140422785566720 DEBUG: CPlayerCoreFactory::GetPlayers(/home/afrase/.var/app/tv.kodi.Kodi/data/userdata/addon_data/plugin.audio.prime_music/temp.mp4)
19:49:06.772 T:140422785566720 DEBUG: CPlayerSelectionRule::GetPlayers: considering rule: system rules
19:49:06.772 T:140422785566720 DEBUG: CPlayerSelectionRule::GetPlayers: matches rule: system rules
19:49:06.772 T:140422785566720 DEBUG: CPlayerSelectionRule::GetPlayers: considering rule: mms/udp
19:49:06.772 T:140422785566720 DEBUG: CPlayerSelectionRule::GetPlayers: considering rule: lastfm/shout
19:49:06.772 T:140422785566720 DEBUG: CPlayerSelectionRule::GetPlayers: considering rule: rtmp
19:49:06.772 T:140422785566720 DEBUG: CPlayerSelectionRule::GetPlayers: considering rule: rtsp
19:49:06.772 T:140422785566720 DEBUG: CPlayerSelectionRule::GetPlayers: considering rule: streams
19:49:06.772 T:140422785566720 DEBUG: CPlayerSelectionRule::GetPlayers: considering rule: dvd
19:49:06.772 T:140422785566720 DEBUG: CPlayerSelectionRule::GetPlayers: considering rule: dvdimage
19:49:06.772 T:140422785566720 DEBUG: CPlayerSelectionRule::GetPlayers: considering rule: sdp/asf
19:49:06.772 T:140422785566720 DEBUG: CPlayerSelectionRule::GetPlayers: considering rule: nsv
19:49:06.772 T:140422785566720 DEBUG: CPlayerSelectionRule::GetPlayers: considering rule: radio
19:49:06.772 T:140422785566720 DEBUG: CPlayerCoreFactory::GetPlayers: matched 0 rules with players
19:49:06.772 T:140422785566720 DEBUG: CPlayerCoreFactory::GetPlayers: adding audiodefaultplayer (PAPlayer)
19:49:06.772 T:140422785566720 DEBUG: CPlayerCoreFactory::GetPlayers: for video=0, audio=1
19:49:06.772 T:140422785566720 DEBUG: CPlayerCoreFactory::GetPlayers: for video=1, audio=1
19:49:06.772 T:140422785566720 DEBUG: CPlayerCoreFactory::GetPlayers: adding player: VideoPlayer
19:49:06.772 T:140422785566720 DEBUG: CPlayerCoreFactory::GetPlayers: added 2 players
19:49:06.772 T:140422785566720 DEBUG: OnPlayBackStarted: CApplication::OnPlayBackStarted
19:49:06.772 T:140421732755200 DEBUG: Thread PAPlayer start, auto delete: false
19:49:06.772 T:140421732755200 DEBUG: PAPlayer::Process - Playback started
19:49:06.773 T:140422135408384 DEBUG: Open - probing detected format [hls,applehttp]
19:49:06.773 T:140422135408384 DEBUG: ffmpeg[7FB6937FE700]: [hls,applehttp] Failed to open segment 0 of playlist 0
19:49:06.773 T:140422135408384 DEBUG: ffmpeg[7FB6937FE700]: [hls,applehttp] Failed to open segment 1 of playlist 0
19:49:06.773 T:140422135408384 DEBUG: ffmpeg[7FB6937FE700]: [hls,applehttp] Failed to open segment 2 of playlist 0
19:49:06.773 T:140422135408384 DEBUG: ffmpeg[7FB6937FE700]: [hls,applehttp] Failed to open segment 3 of playlist 0
19:49:06.773 T:140422135408384 DEBUG: ffmpeg[7FB6937FE700]: [hls,applehttp] Failed to open segment 4 of playlist 0
19:49:06.773 T:140422135408384 DEBUG: ffmpeg[7FB6937FE700]: [hls,applehttp] Failed to open segment 5 of playlist 0
19:49:06.773 T:140422135408384 DEBUG: ffmpeg[7FB6937FE700]: [hls,applehttp] Failed to open segment 6 of playlist 0
19:49:06.773 T:140422135408384 DEBUG: ffmpeg[7FB6937FE700]: [hls,applehttp] Failed to open segment 7 of playlist 0
19:49:06.773 T:140422135408384 DEBUG: ffmpeg[7FB6937FE700]: [hls,applehttp] Failed to open segment 8 of playlist 0
19:49:06.773 T:140422135408384 DEBUG: ffmpeg[7FB6937FE700]: [hls,applehttp] Failed to open segment 9 of playlist 0
19:49:06.773 T:140422135408384 DEBUG: ffmpeg[7FB6937FE700]: [hls,applehttp] Failed to open segment 10 of playlist 0
19:49:06.773 T:140422135408384 DEBUG: ffmpeg[7FB6937FE700]: [hls,applehttp] Failed to open segment 11 of playlist 0
19:49:06.773 T:140422135408384 DEBUG: ffmpeg[7FB6937FE700]: [hls,applehttp] Failed to open segment 12 of playlist 0
19:49:06.773 T:140422135408384 DEBUG: ffmpeg[7FB6937FE700]: [hls,applehttp] Failed to open segment 13 of playlist 0
19:49:06.773 T:140422135408384 DEBUG: ffmpeg[7FB6937FE700]: [hls,applehttp] Failed to open segment 14 of playlist 0
19:49:06.773 T:140422135408384 DEBUG: ffmpeg[7FB6937FE700]: [hls,applehttp] Failed to open segment 15 of playlist 0
19:49:06.773 T:140422135408384 DEBUG: ffmpeg[7FB6937FE700]: [hls,applehttp] Failed to open segment 16 of playlist 0
19:49:06.773 T:140422135408384 DEBUG: ffmpeg[7FB6937FE700]: [hls,applehttp] Failed to open segment 17 of playlist 0
19:49:06.774 T:140422135408384 ERROR: ffmpeg[7FB6937FE700]: [hls,applehttp] Error when loading first segment 'https://d2lg00fehdyg04.cloudfront.net/0269d550-c200000304607865%2F5b1f2c7e-a0cb-38ab-98e4-55f3fd539992.ts?response-content-disposition=attachment%3B%20filename%3D%225b1f2c7e-a0cb-38ab-98e4-55f3fd539992.ts%22&Expires=1545851710&Signature=RPfj7YBGFdmKsX-QOGIHdBQA0fHAZND0RLt92voOJjDC08iClw9t1jISPvl7gBK~LZetcqMBXPj0X4YXCrPTZFTaRYHPb704Hfag51v1gRFlTInjQ7~tgZP0tkKSWLWyNBNRlguT0U9wK1QCqbew7QITNYC7Iqa0s8iymu-hvOA_&Key-Pair-Id=APKAJVZTZLZ7I5XDXGUQ'
19:49:06.774 T:140422135408384 ERROR: Open - Error, could not open file /home/afrase/.var/app/tv.kodi.Kodi/data/userdata/addon_data/plugin.audio.prime_music/temp.mp4
19:49:06.774 T:140422135408384 ERROR: Init: Error creating demuxer
19:49:06.774 T:140422135408384 ERROR: CAudioDecoder: Unable to Init Codec while loading file /home/afrase/.var/app/tv.kodi.Kodi/data/userdata/addon_data/plugin.audio.prime_music/temp.mp4
19:49:06.774 T:140422135408384 WARNING: PAPlayer::QueueNextFileEx - Failed to create the decoder
19:49:06.774 T:140422135408384 DEBUG: OnAVStarted: CApplication::OnAVStarted
19:49:06.774 T:140422135408384 DEBUG: OnQueueNextItem: CApplication::OnQueueNextItem
19:49:06.775 T:140422785562368 DEBUG: CAnnouncementManager - Announcement: OnAVStart from xbmc
19:49:06.776 T:140422785562368 DEBUG: GOT ANNOUNCEMENT, type: 1, from xbmc, message OnAVStart
19:49:06.776 T:140421724362496 INFO: Python interpreter stopped
19:49:06.777 T:140421724362496 DEBUG: Thread LanguageInvoker 140421724362496 terminating
19:49:06.788 T:140422785566720 DEBUG: CMusicGUIInfo::InitCurrentItem(plugin://plugin.audio.prime_music/?mode=playTrack&asin=B07JKCGZY2&name=Jingle+Bells&thumb=https%3A%2F%2Fimages-eu.ssl-images-amazon.com%2Fimages%2FI%2F51Wrv1WM-qL.jpg&artist=Gwen+Stefani&album=You+Make+It+Feel+Like+Christmas+%28Deluxe+Edition%29)
19:49:06.790 T:140422785566720 DEBUG: Loading additional tag info for file plugin://plugin.audio.prime_music/?mode=playTrack&asin=B07JKCGZY2&name=Jingle+Bells&thumb=https%3A%2F%2Fimages-eu.ssl-images-amazon.com%2Fimages%2FI%2F51Wrv1WM-qL.jpg&artist=Gwen+Stefani&album=You+Make+It+Feel+Like+Christmas+%28Deluxe+Edition%29
19:49:06.790 T:140422785566720 DEBUG: CPlayerGUIInfo::InitCurrentItem(plugin://plugin.audio.prime_music/?mode=playTrack&asin=B07JKCGZY2&name=Jingle+Bells&thumb=https%3A%2F%2Fimages-eu.ssl-images-amazon.com%2Fimages%2FI%2F51Wrv1WM-qL.jpg&artist=Gwen+Stefani&album=You+Make+It+Feel+Like+Christmas+%28Deluxe+Edition%29)
19:49:06.790 T:140422785562368 DEBUG: CAnnouncementManager - Announcement: OnChanged from xbmc
19:49:06.790 T:140422785562368 DEBUG: GOT ANNOUNCEMENT, type: 1024, from xbmc, message OnChanged
19:49:06.791 T:140422785562368 DEBUG: CAnnouncementManager - Announcement: OnPlay from xbmc
19:49:06.791 T:140422785562368 DEBUG: GOT ANNOUNCEMENT, type: 1, from xbmc, message OnPlay
19:49:06.890 T:140422785566720 DEBUG: ------ Window Init (DialogBusy.xml) ------
19:49:06.892 T:140422785566720 DEBUG: StartScript - calling plugin Amazon Prime Music('plugin://plugin.audio.prime_music/','5','?mode=playTrack&asin=B07JK2X18L&name=Let+It+Snow&thumb=https%3A%2F%2Fimages-eu.ssl-images-amazon.com%2Fimages%2FI%2F51Wrv1WM-qL.jpg&artist=Gwen+Stefani&album=You+Make+It+Feel+Like+Christmas+%28Deluxe+Edition%29','resume:false')