Bob,
Per our conversation, there are three options for selling only to preferred Milestone partners/ISVs:
1. Use whatever built-in marketplace Milestone provides to plugin developers and sell exclusively via that platform.
2. Add in a checkpoint in the purchase workflow on the e-commerce website which prompts a customer for their Milestone ISV or partner number (which will be validated real-time against an API endpoint which Milestone will provide) and prevents checkout if the number is not valid.
3. Prevent users from checking out unless they are logged in with a Milestone account. This would require integrating with the Milestone login server using a single-sign on mechanism. I am not sure if this is an option, but that would effectively limit the audience to customers with a Milestone login – and hopefully, there would be a way to distinguish between someone who just has a Milestone login and someone who is an ISV/Partner. But, this is a question for them.
Of the three options, scenario 2 or 3 provide the most elegant solutions, but in both cases, they rely on something being in place on the Milestone side of things. Given that this is likely not the first time such a question has been raised with them, I’d hope they already have something in place – similar to Apple, Google or Microsoft – who all have ISV/Partner programs.
Lucas.