BT Home Hub 5A: tvheadend configuring IPTV

I just discovered that BT Home Hub 5A provide both udpxy and tvheadend together with ffmpeg. I'm trying to configure openWRT as IPTV relay that receives the stream from Internet and transmit to the LAN network.
I read some information about tvheadend and IPTV here and here and about openWRT multicast/IGMP here.
I tried to use one of the free IPTV service provided here, but I was not able to setup ip into openWRT.
The same configuration works well under ubuntu mate 16.04 LTS. The only difference is the version of tvheadend: openWRT 4.0.10 while ubuntu mate 4.3-1288.
Log file logread | grep tvheadend

Tue Jul 10 14:44:00 2018 tvheadend[2668]: mpegts: http://IP&type=m3u&output=ts in IPTV - scan no data, failed
Tue Jul 10 14:44:00 2018 tvheadend[2668]: subscription: 0004: "scan" unsubscribing

Do you have any suggestion?
Thank you

P.S. of course I have to avoid transcoding otherwise it would not be possible.