startPurchase method
Start a purchase.
Implementation
Future<void> startPurchase(String productID) async {
for (var prod in _products) {
final purchase = _hasPurchased(prod.id);
if (purchase != null) {
// Already purchased
await _deliverProduct(purchase);
} else if (prod.id == productID) {
await _buyProduct(prod);
}
}
}