If the total amount of unitprice of orderItems in multiple items exceeds the amount set in amount, will an error occur in the system? If there is no error, is the amount actually traded the amount in the amount item? If 0 is not allowed in the unit price

An error does not occur because the validation that compares the amount of the unit price of the orderItems item and the amount is not performed.

The amount actually traded is the amount in the amount item.If there is a merchant that wants to set 0 yen, it can be avoided by setting 1 yen.

Also, as a workaround, it is possible to not include the items of orderItems in the request body.