People can't hear me on calls via car cassette aux with iphone 16 pro max.

One of our cars that I mostly drive, is older and in order to listen to music from my phone, I use a cassette aux adapter. I recently upgraded from the iphone 14 plus to 16 pro max and have discovered that when trying to call someone/ someone calls me, they cannot hear me when I'm using this. I have tried using 2 different usb-c to audio cables and it happens with both. When I first plug in the audio cable, it asks me if i'm using headphones or an "other source" and I've been choosing headphones. I never had it ask me this on my iphone 14 plus. Is there something I am missing or doing wrong? Thank you!!