Online casinos enhance payment transaction security through various measures, such as using encryption technologies like Secure Socket Layer (SSL) to safeguard data, tokenization to replace sensitive information with unique identifiers, and multi-factor authentication (MFA) for additional verification. They also perform regular security audits and compliance checks to adhere to industry standards. By integrating these technologies and practices, online casinos strive to ensure a secure environment for financial transactions and protect players' sensitive data from breaches.