Microphone not working in Garageband when headphones plugged in

I have an iPhone 15 pro. I recorded a piano track in GarageBand, and now I’m trying to add the vocals. The input says Mic, but when I have the headphones plugged in, nothing registers. If I unplug the headphones, I can see the sound register on the monitor.

Never had this problem before. This is probably the first time I’ve done this since I went from the iPhone 11 to the 15.