The rapid growth of digital payment ecosystems, which include mobile wallets, UPI platforms, online banking channels, and merchant-integrated gateways, has led to a big rise in both the number of transactions and the complexity of financial fraud. Standard systems for finding fraud mostly use rule-based methods or independent transaction-level classifiers. These systems can't pick up on the complicated relational and temporal dependencies that are common in modern fraud patterns. This research presents a Graph Neural Network (GNN)-based real-time fraud detection framework that conceptualizes the digital payment ecosystem as a dynamic, multi-relational graph consisting of users, devices, merchants, IP addresses, and transactional interactions. The framework combines Relational Graph Convolutional Networks, Graph Attention Networks, and Temporal Graph Networks to learn behavioral patterns that change over time, in context, and in structure. A hybrid supervised–unsupervised scoring module is used to figure out how likely fraud is. This module can find both known and new types of attacks. A lot of tests on big synthetic payment datasets show that the proposed model does much better than traditional machine learning and deep learning baselines in terms of AUC-ROC, precision, and F1-score. It also has an inference latency of less than 50 ms, which makes it good for real-time use. The results show that GNN-based methods are effective for next-generation financial systems that need to be safe, scalable, and smart when it comes to stopping fraud.