We are currently integrating with a payment provider wherein we send some request and get some response.
The payment provider then does a callback and posts the status after some time for the request that was sent to my global Rest API where its gets authenticated and gets processed further.
We have developed it as a managed product and packaged it. The Apex Rest API class is exposed through public site which should be configured in Subscriber org.
Now we want to work out this whole product for customers which uses Professional edition. We don't have sites in PE orgs. What is the work around? I can think of having a external app which takes a request and then sends data to Salesforce.