HTTPS works fine except on iPhone. Safari won't open the site and complains that it doesn't support TLS 1.2, but I've checked that it does indeed support TLS 1.2.
I went to SSL Checker to try to figure out the problem, and everything seems ok, except it also says: "Server certificate is not trusted by reputable certificate stores!"
The Certificate paths section has three steps, first two are ok, third one has an error:
"Extra download Not in trust store".
ISRG Root X1 (self-signed)
RSA 4096 bits / SHA256withRSA
Not sure about what to do. Thankful for any help.
My domain is: athletium.app
My web server is (include version): IIS 10
The operating system my web server runs on is (include version): Windows Server 2019
My hosting provider, if applicable, is: Hostwinds, VPS
I can login to a root shell on my machine (yes or no, or I don't know): Yes
I'm using a control panel to manage my site (no, or provide the name and version of the control panel): No
The version of my client is (e.g. output of
certbot --version or
certbot-auto --version if you're using Certbot): WinACME v188.8.131.52