You are using the wrong credentials (merchant ID/ portfolio ID / password), please verify you are using the credentials as provided by AfterPay.
The phone number is missing or has an invalid value.
The postal code is invalid. Please make sure the postal code is the correct format, matching the ISO country code.
The sum of the amounts of the orderlines does not match the totalOrderAmount. Usually, this is due to rounding errors.
The ordernumber has already been registered (must be unique in a portfolio ID). This usually happens if you are trying to authorize the same order again, using the same ordernumber.
Please keep in mind that the ordernumber is registered with resultID 0 and resultID 3. In those cases, you need to use another, unique, ordernumber. With resultID 1 or 2, the ordernumber is not registered and can be used again. Best practice is to always use a new ordernumber with each authorization.