Or, one could test in production-parallel deployment. Clone all requests to a parallel test system, use the same production data for enrichment and validation f

Or, one could test in production-parallel deployment. Clone all requests to a parallel test system, use the same production data for enrichment and validation for both, the current production system and the new one. And automatically compare the outputs from both systems for those fields that have to be the same between the systems, and test the expected changed outputs automatically. Once there are no errors in the new system, you start switching over the systems in a controlled manner where the new system increasingly takes on the production role, and the old one still processes cloned requests for a while as a sanity check… This way you don’t need an unrealistic staging environment, and you are not introducing any errors into production. It worked more than 20 years ago when I architected this for a system that had to process 50M transactions every hour.