Access Management Solution for Digital Products

I own three distinct digital products, each hosted on different platforms. I need a professional who can research and propose a solution that grants access to these products upon the purchase of any one of them.

Key Requirements:
- Expertise in digital product management and access control systems
- Proficiency with various digital platforms
- Strong research skills to find a feasible solution
- Excellent understanding of e-commerce and digital product delivery

Please note, each of these products operates on a different backend. A comprehensive understanding of backend systems will be beneficial. I am looking for a highly skilled freelancer who can handle this task efficiently.

I have 3 products / Services I sell to my users. They all use different backends for user management and billing.

My goal is for a user to purchase any of my products and get access to the remaining products.

Here's an example.

User 1 buys product 1
They get access to products 2 and 3

User 2 buys product 2
They get access to products 1 and 3

If user cancels, they get removed from all products

My products use the following backends
Product 1: extensionpay.com / stripe
Product 2: beehiiv.com / stripe
Product 3: kartra.com / stripe (user pays for facebook group access, we'll have to add and remove users)

Once the research is done I'm looking to have the project built by you or another team.

This project is strictly for the RESEARCH, a follow up project will be posted to build the proposal.