Some of the cheaper or newer SSL suppliers will require this to work properly (otherwise you may be prompted that the cert is invalid when it's not the case but it will certainly scare off your users!).
In the Apache vhost conf for the domain here is what you add:
Here is a full example of an SSL Vhost config in Apache using a CA Certificate file
I spent so much time debugging this, most sites don't tell you a very important option to use with CURL and you will only find out this is the problem by running the PHP script from the command line you get the following output that shows the issue (I don't see any way to get this output from Apache itself).
* About to connect() to ip.ip.ip.ip port 25000
* Trying ip.ip.ip.ip... * connected
* Connected to ip.ip.ip.ip (ip.ip.ip.ip) port 25000