iPhone 12 Pro Max don't recognize that an AUX cord is plugged in

I bought a new iphone 12 pro max and plugged it into my aux cord and it would play music through my speakers in my truck. I had to get a new aux cord because my other one got lost and now my iphone will not even recognize that I have an aux cord plugged into it. Please help! I cant listen to music now in my truck

[Re-Titled by Moderator]