AU-520M, SmartSDR and no transmit power output

Using SmartSDR on my Windows 11 pc, I can see the microphone audio level meter move while speaking into the microphone. But, no power output indicated. RF power slider at maximum. PC audio selected in upper right corner of SmartSDR. PC selected for the microphone input. Clicking on MOX, speaking into microphone, plenty of audio. But, no indication of actual power output. I have rebooted the radio and the computer. Same results. If I turn the Tune Power slider all the way up, and click on Tune, I get over 500 watts indicated on the power meter. I have no problem transmitting with a microphone connected to the radio while using the front panel. I have checked Windows Firewall and it has given SmartSDR full permissions. I figure it's something simple. But, for the life of me I don't see what it is. My microphone is a Behringer 8500 Dynamic microphone hooked to a Focusrite USB audio interface. It works fine with a Anan 8000DLE and Thetis. So, I don't think it is a hardware issue.

James

WD5GWY