toString method
Return the contents of this class as a string
Implementation
@override
String toString() {
return 'identifier: $identifier, '
'type: $type, '
'numberOfPeriods: $numberOfPeriods, '
'price: $price, '
'localizedPrice: $localizedPrice, '
'paymentMode: $paymentMode, '
'subscriptionPeriod: $subscriptionPeriod, ';
}