The core concept of Gateway Protocol service is to allow merchants to use legal currency and cryptocurrency payments in the same service no matter what settlement system they choose. The integrated payment system ensures transaction transparency by recording and providing data and statistics so that merchants and users can check transaction details and important information. In addition, Gateway Protocol implements a cryptocurrency payment interface that does not lag behind legal currency payments by adopting extensive user experience in legal currency payments. By supporting various simple payment methods such as Barcode payment, and QR code payment such as MPM(Machine Presented Mode), and CPM(Customer Presented Mode), Gateway Protocol minimizes infrastructure demand such as POS from merchants, ensure an easy transition to Gateway Protocol Payment Service.