sonarr installation

Hey i keep getting this when trying to install sonarr.
Seems to be something wrong with downloading mono?

Get:1 stretch InRelease [5,863 B]
Ign:1 stretch InRelease
Hit:2 stretch InRelease
Hit:3 stretch InRelease
Fetched 5,863 B in 1s (4,573 B/s)
Reading package lists… Done
W: GPG error: stretch InRelease: The following signatures couldn’t be verified because the public key is not available: NO_PUBKEY A6A19B38D3D831EF
W: The repository ‘ stretch InRelease’ is not signed.
N: Data from such a repository can’t be authenticated and is therefore potentially dangerous to use.
N: See apt-secure(8) manpage for repository creation and user configuration details.
[Info] Running apt simulation to check for errors, please wait…
E: Unmet dependencies. Try ‘apt --fix-broken install’ with no packages (or specify a solution).
[Failed] Apt simulation | An issue has occured

[Failed] The apt cache may be corrupt, apt mirror offline, or you have held broken packages. DietPi-Software will now exit.