Hello, I can surely help you to create a group buy service to add members via proxy.
I have experts having more than 7+ year of experience in PHP, Cake PHP, Joomla, Magento, Shopify, and so on.
If you want I can provide you a demo of my previous work.
I really feel like this is my job and I really look forward to having a detailed discussion.
Thankyou
Kuldeep