When you see a subdomain like io-sm-log.tantanapp.com, the first question is whether it belongs to something you should trust. This one is part of Tantan, a well-known Chinese dating app with millions of users. The subdomain itself acts as a reverse proxy server, meaning it handles backend traffic for the app rather than being a consumer website you'd log into.
For a piece of infrastructure, the site does a lot right: it has an about page, legal disclosures, privacy policy, and terms of service. Those are strong signs that the company behind it takes compliance seriously. The SSL certificate is valid and uses modern TLS encryption, but the server still accepts very old, insecure versions of TLS (1.0 and 1.1). That's a gap you wouldn't see from top-tier services, but it doesn't make the site dangerous by itself.
If you're wondering whether io-sm-log.tantanapp.com is legitimate, the answer is almost certainly yes — it's simply a technical endpoint for Tantan. You wouldn't visit this URL directly, and you don't need to worry about scammers hiding here. The real question is whether the main Tantan app is safe to use, which is a separate review. For this subdomain, the evidence says it's mostly safe, with the caveat that the outdated TLS support should be fixed.