Confinity is the company that developed the PayPal website that survived that merger. Elon Musk was not on the Confinity side, he was trying to pivot his x.com bank into a PayPal clone and buy users ($30 per signup) faster than them until they merged to avoid running each other out of cash. The two startups were operating out of the same building at the time. After the merger, Musk was named CEO but ousted from the company just 5 months later, in part for being absent much of the time (including at the time of his firing), and in part because the PayPal engineers had circulated a petition to the board asking them to remove him. The board agreed.
Co-founder is just a marketing name and has no meaning in reality, actions do. Looking at this he provided in money which was likely to ruin his business by overspending it and greater minds prevailed in the end (I'm not saying paypal is a good thing or not). Why they made him CEO I cannot fathem but it has probably something to do with the bullying behaviour he is known for.
I've been named co-founder once but as soon as its usefulness ran out it got removed from the website (nothing else changed).
