Automattic: IDOR able to buy a plan with lesser fee

Summary IDOR allows you to pay with the same amount but different currency. For example, paying 35000$ instead of 35000€ Steps To Reproduce 1. Go to https://account.mailpoet.com/ and select a plan 2. For example I have selected this plan; https://account.mailpoet.com/orders/new?p=214 3. Now, as y...