I put the file downloaded from https://curl.haxx.se/ca/cacert.pem into C:\Program Files\PHP\v7.2\extras\ssl and edited the php.ini file and put curl.cainfo = C:\Program Files\PHP\v7.2\extras\ssl\cacert.pem
You then need to run iisreset from an elevated command prompt.
I host my own server. What do I need to look at? It is hosted on a Windows 2016 and IIS. It has a valid cert issued by CertifyTheWeb.