Using gr.Audio in "upload" mode fails on a simple test

I’m trying to use gr.Audio where I upload a file and print “hello” to the output. It seems to fail.

import gradio as gr

def greet(aname):
    return "hello"
  
input_audio = gr.Audio()
demo = gr.Interface(fn=greet, inputs=input_audio, outputs="textbox")
    
if __name__ == "__main__":
    demo. Launch()