User Acceptance Testing (UAT) is a significant component of cloud billing system. It does this by ensuring that in a hybrid Azure environment, the system functions properly, that financial calculations are correct and that it adheres to all rules prior to launching. This paper discusses the use of Postman to automate tests and also reasons why the use of the JSON payload format should be adopted to raise the accuracy of UAT. Acceptance of complex API responses reduces human errors and shortens billing data, tax evaluation and adjustment approval. The method ensures that there is a strong connection between the back-end logic and the business expectations and give the stakeholders and QA engineers a chance to work effectively together in the process of validation. Evaluations indicate that the speed, precision and reliability of the billing procedure have greatly increased. The results show that UAT based on automated JSON validation not only minimizes the time of testing but also increases the reliability and the credibility of cloud-based financial applications.