OSMC update doesn't work


I’m running this version of OSMC:

grep Kodi .kodi/temp/kodi.log | head -3
18:37:51.431 T:1926257152 NOTICE: Starting Kodi (17.6). Platform: Linux ARM (Thumb) 32-bit
18:37:51.431 T:1926257152 NOTICE: Using Release Kodi x32 build (version for Raspberry Pi)
18:37:51.431 T:1926257152 NOTICE: Kodi compiled Dec 31 2018 by GCC 6.3.0 for Linux ARM (Thumb) 32-bit version 4.9.30 (264478)

I tried to do an update from the console and I got this error:

sudo apt-get update
Hit:1 http://security.debian.org stretch/updates InRelease
Ign:2 http://ftp.fau.de/osmc/osmc/apt stretch InRelease
Ign:3 http://ftp.debian.org/debian stretch InRelease
Err:4 http://ftp.fau.de/osmc/osmc/apt stretch Release
Something wicked happened resolving ‘ftp.fau.de:http’ (-5 - No address associated with hostname)
Hit:5 http://ftp.debian.org/debian stretch-updates InRelease
Hit:6 http://ftp.debian.org/debian stretch Release
Reading package lists… Done
E: The repository ‘http://apt.osmc.tv stretch Release’ does no longer have a Release file.
N: Updating from such a repository can’t be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details

This is the content of my /etc/apt/sources.list

deb http://ftp.debian.org/debian stretch main contrib non-free
deb Index of /debian stretch-updates main contrib non-free
deb http://security.debian.org/ stretch/updates main contrib non-free
deb http://apt.osmc.tv stretch main

Do you have idea what can be wrong?

Many thanks in advance