Hi Lorenzo,
PlayIt Cartwall will play out to the selected sound card you have selected under File > Settings. If you want to play audio into Discord you would need to route the audio played out of PlayIt Cartwall through a virtual mixer such as Voicemeeter Banana (https://vb-audio.com/Voicemeeter/banana.htm) and then have Discord listen to this mixed output.
Lorenzo Lewin
It doesn't works in discord... somebody halp?