1. user uses IP to access the server via https (example https://188.8.131.52 - but http://184.108.40.206 is not affected!)
2. or user uses https with self-signed certificate for domain (example https://my_domain.com - but again http://my_domain.com unaffected)
3. or user uses outdated/invalid certificate for https connection.
That is not TSplus issue but pure invention of Apple to stop any potential hacker activities on iOS/Mac devices when the secured connection authority(https certificate) can't be verified.
To fix this issue you have few different ways how you may proceed.
1. buy domain(example https://my_domain.com) and sign it by authority(example Let's Encrypt etc.), that is what Apple expects from you to do.
2. or use http address (insecure, if only port 443 used then try http://my_domain.com:443/ - No SSL redirection allowed!)
3. or install self signed certificate on iOS/Mac device directly. (very tricky indeed)
4. or use another browser (at least possible for Mac but not possible for iOS!)
Remark: under specific circumstances the IPs can be signed, but smarter it would be to buy domain and sign it for free.