Airplay audio to airport express works from iphone but not from M1 Pro (Sonoma)

As the title says. I have an airport express 2nd generation that is configured to join my existing (non-Airport) wireless network. I have it connected to some external speakers. I can stream audio to it from my iPhone without issue. When I try to stream audio from my M1 Pro macbook, it gives me an error message "Could not connect to XXX". It worked briefly from my macbook when I initially set it up. I've tried restarting the airport express and updating the firmware but it still cannot play from my macbook. What could the issue be / how do I fix this?