Improve coupon per party using payment data
When external users can register their party and the company share coupons per party, external users can cheat the system by creating new party to reuse the coupon. This can be mitigated if we count coupon grouped by all the parties the users has created. We can link together parties if they have been used the same payment method. When using Stripe we can use the fingerprint of the payment method (when available) to group parties. When using Braintree we can use the customer id.