demokueski.sandbox.mambu.com is a subdomain on Mambu's sandbox environment, which banks use for testing their core banking software. That explains most of what you see — or don't see. There's an about page and legal disclosures, which is unusual for a test environment and suggests the company takes compliance seriously even here. But there's no contact info, no social media, and no brand favicon, because this site isn't meant for customers.
For a development sandbox, the security setup is solid: HTTPS with HSTS, clickjacking prevention, and a content security policy. The SSL certificate is valid but renews in about two weeks, so keep an eye on that if you're integrating via API. The site isn't on any blacklists and loads quickly.
So is demokueski.sandbox.mambu.com a scam? No — it's a legitimate test environment. But it's not a consumer website, so don't expect customer support or a storefront. If you landed here by mistake, you're likely in the wrong place. For developers working with Mambu, it's a functional sandbox.