Flat discount is for a currency other than that of the transaction

You are attempting to apply a flat discount that has a different currency to that of the transaction

Error Message	`Flat discounts must be in the same currency as the transaction. Discount currency: %s, Transaction currency: %s`
Error Code	`transaction_invalid_discount_currency`
Status Code	`400`

Common causes

The flat discount you are trying to add to the transaction has a different currency code than the transaction itself

Ensure the currency code on the discount provided matches that of the transaction