So it appears that most Prop Firms have dropped PayPal as a payment processor as they are experiencing PayPal Chargeback scams. This is when traders are failing the challenges and then claiming a chargeback from PayPal to get their money back. When the Prop Firm challenges PayPal, PayPal are taking the side of the trader/consumer. This malpractice is not only being carried out by traders with Prop Firms but also many other businesses. A quick search on Google uncovers this practice.
https://www.paypal-community.com/t5/How-to-use-PayPal-Archive/CHARGEBACK-SCAM-SELLERS-BEWARE/td-p/27035
This is actually from the PayPal website, they dont seem particularly interested in supporting the businesses.