I may be missing something but it looks like this is a bug related to this functionality:
Steps to reproduce issue:
1. I create a BXGY discount with code 'bogo' and a 'Minimum quantity of items' requirement
2. I get the discount using the API successfully
3. I update the discount above to use the 'Minimum purchase amount'
4. I hit the same endpoint to get the discount and get back a 404.
5. Revert the change, hit the endpoint, get 200 again.