At present OptimizePress does not have a specific integration with 2Checkout. Our OptimizeMember membership platform integrates with a number of gateways including Paypal, Authorize.net and Infusionsoft, but not currently 2Checkout.
You can still link to a 2Checkout checkout or order page from your OptimizePress pages using a normal hyperlink but we do not have any integrations with our membership systems currently.