epamsystems.sandbox.mambu.com is a subdomain that lives under Mambu, a well-established cloud banking platform used by financial institutions worldwide. The 'sandbox' part tells you this is a testing or development environment, not a consumer storefront. That explains a lot about what you see and don't see here.
Security is handled properly: HTTPS is on, browser protections are active, and there are no blacklist warnings. The site also posts a privacy policy, terms of service, and an official business disclosure. These are the basics that any legitimate commercial subsidiary should have, and this one does.
There are no user reviews for this sandbox, which is expected — you don't usually review a development environment. If you're an EPAM employee or a Mambu customer working with their sandbox, this URL is almost certainly part of that legitimate workflow. If you're a random visitor, there's nothing here to buy or sign up for, so no risk either way. The signals point to a real piece of infrastructure, not a scam.