I have a Z7+ box. Some of the TV series my IPTV provider offers do not play in MyTV Online.
As an example, there are five Viking series. Series 1,2,3 and 5 give the error message " Can't play this video. Please try again later". Bizarrely Series 4 plays OK.
My provider tells me all series play OK on other platforms. I can confirm this as I also use the service with VLC and Kodi on PC.
However I think MAG boxes may have a similar issue.
I installed the Kodi app on the Formuler Z7+ and loaded my suppliers zip file to enable their package. All the Viking series played OK through Kodi. So it's not a problem my supplier feels they should resolve.
Does this suggest there may be a codec issue in MyTv Online?