I found an answer(Thanks to L29Ah from #sigrok IRQ channel). I needed to digitize the channel first (Channel->conversion), once this was done I was able to connect it to the decoder.
However it seems like I can onle decode very short messages because the sample rate is mot high enough. Is this a hardware limitation of my scope(1GSa/s)? or is it because it is connected to PulseView via Ethernet?