As the integration of Internet of Things (IoT) devices into Software-as-a-Service (SaaS) platforms expands, security concerns in digital environments have grown significantly. Traditional public key cryptographic schemes, including Diffie-Hellman (DH) and Elliptic Curve Cryptography (ECC), face high computational demands and key management vulnerabilities, which are exacerbated in resource-constrained environments like IoT devices and edge modules. To address these challenges, we propose a Hybrid KeyCryptographic Engine (HKCE), coupled with a Memory-Based Lightweight Tokenization(MBLT) approach for enhanced access authentication in Payment Transaction Systems(PTS). This hybrid cryptographic framework optimises encryption processes, mitigates bandwidth vulnerabilities, and offers quantum-resistant resilience against emerging cryptographic threats. The performance of the proposed HKCE-MBLT solution is benchmarked against traditional ECC-Key Scattering Schemes (ECC-KSS), demonstrating a significant reduction in computational overhead (25% compared to 75% forECC-KSS), higher throughput (78.57% compared to 21.43% for ECC-KSS), and lower bandwidth vulnerability, while maintaining the integrity, confidentiality, and availability of transactions. Our solution provides a scalable, efficient, and secure framework that ensures privacy and trust in IoT-enabled SaaS systems, positioning it as a robust alternative for securing payment card systems and other sensitive applications in the evolving digital landscape.