Pro Forms/ssl certificate on prime domain serving subdomains
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I have just purchased a single-site license for S2Member Pro to set up a subscription system for my online arts magazine: http://berkshirereview.net. This domain is actually a subdomain of http://artspress.com, which has other subdomains which might someday also require paid subscriptions, but for the moment I am only concerned with berkshirereview.net, and I have S2Member Pro set up on it. My host will allow ssl certificates only for the primary domain.
My question is, what is the best way to use artspress.com to manage the subscriptions of berkshirereview? Should I upgrade to an unlimited-site license, install S2Member on both sites and keep the forms for berkshirereview.net (and other subdomains, when the time comes) on arts press.net, or is there a way to make it work with the single-site license, moving it to arts press.net and redirecting payment from berkshirereview.net?
My question is, what is the best way to use artspress.com to manage the subscriptions of berkshirereview? Should I upgrade to an unlimited-site license, install S2Member on both sites and keep the forms for berkshirereview.net (and other subdomains, when the time comes) on arts press.net, or is there a way to make it work with the single-site license, moving it to arts press.net and redirecting payment from berkshirereview.net?