package is not maintained and there's some issues needs to be fixed.
- enhance issue too many requests for amazon server (429)
lib/Helpers/SellingPartnerApiRequest.php
- fix DateTime to string
lib/Models/Finances/ShipmentEvent.php
change postedDate to string
- add DateTime class for finance Models.
add DateTime class to avoid crash in package.
ClouSale\AmazonSellingPartnerAPI\Models\Finances\DateTime.
- fix upgrade to php7.4
parent not in scope pulling changes from clousale#138