Good day,
I will gladly help you with your project. I have the required JavaScript and Node skills to accomplish this task. However, I have the following questions:
1. Just that I understand the project correctly, you don't want to share something, but rather check if the users shared your information?
2. Do the user need to share to all three (Facebook Profile, Facebook Group and Instagram) to get the discount?
3. To which Facebook Group do they need to share the info?
4. Should the user and their share info be saved to a database?
5. How should the user be informed when he gets the discount (e.g. by email or through a website)?
I will develop the initial version and thereafter you can give feedback until you are happy. If you have any questions, do not hesitate to contact me.
Greetings
Matthias