Building a Scalable Digital Membership Card System for Large Organizations

Hello Developers I am exploring how to build a scalable digital membership card system for large organizations and would really appreciate guidance from this community. I am trying to understand how such systems can be designed and implemented in a scalable and secure way. The idea is to allow organizations to issue and manage digital membership cards with features like secure member authentication, API based integration with external systems, QR code based validation, mobile wallet support for digital cards, and a central dashboard for managing memberships at scale. While researching, I came across platforms like MembershipAnywhere that offer digital membership card and member management solutions for large organizations, which helped me understand the possible scope of such systems. What I have done so far is design a basic API flow for issuing membership cards, build a simple prototype for QR based validation, and start researching token based authentication systems. Where I need help is understanding scalable architecture for large scale membership systems, best practices for secure QR or token based validation in real time, how such systems handle synchronization across multiple devices and platforms, and what tools SDKs or design patterns are commonly used for this type of product. I am building this for learning and system design understanding and not for any commercial purpose at this stage. Any guidance from developers who have worked on similar systems would be really helpful