Installing Transmission error

[Katherine Young]

Hi, 
I was trying to install the Transmission Flatpak but i'm getting this error:
error: Failed to install org.gnome.Platform/x86_64/3.30: Can't pull from untrusted non-gpg verified remote


I'm using Linux Endless OS 3.5.3 
Transmission has been deleted from the App Center and I've been trying to find a torrent client that I can use.
I'll attach a screenshot of the command error.

Looking forward to your reply.
K.

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