USB Audio Player Pro connection

Hello everyone,
Just bought my Plex Pass so I can use Plexamp and stream my music to my phone.

For the best playback I use USB Audio Player Pro to connect to a Audioquest Dragon external DAC.
My problem is that I cannot make a connection between Plexamp and the USB Audio Player Pro.
I’m kind of stuck here.
Any suggestions?

Well, you can’t.

Thanks!
Still stuck, but that’s life