No payment page for Pro Sites

Is there any documentation on how to set up Pro Sites correctly?

My specific problem which I’ve not been able to find a forum post for is how members pay. My registration process works fine. New members signup, get the activation email and can log into their dashboard. However I can’t work out how they then pay? The only thing I can see when I try it myself is an upgrade button on the top admin bar. However this just takes me to a https version of my home page. There’s no payment boxes or buttons to then take them to paypal. I’m sure my configuration is wrong somewhere but I’m not sure where.

Many thanks,