Promio is designed to facilitate not only your visitors purchasing from you but them sharing it with their audience.
In rare cases, a very small percentage of visitors will choose to share the code, goto facebook and not complete the share. They will still be able to see the code.
Over 98% of customers will complete the whole process by sharing your store/products and using the code.
Its a win/win either way for your store which makes Promio a great app.