external hardware configuration issue

Hi everyone,
can’t find a solution trying to connect a presonus studio channel as an external effect in cubase 9.
I’ve a Steinberg UR824 soundcard. I’ve connected the output n.8 in the input of presonus and the output of presonus in the input 8 of UR.
Then in “VST connections” i created an external effect with a mono send (output 8) and a mono return (input 8)
When i load the effect as an insert i can’t hear anything. I also tried to load an external channel with a send but no sound is coming.
What i’m missing?

Thanks in advance