Using Paypal .NET SDK 1.9.1 If I do: new Transaction() { description = "My description", invoice_number = "INVOICE-001", amount = amount, item_list = itemList } everything works as expected. However, if I change the format of the invoice_number to anything other than INVOICE_XXX where XXX is exactly 3 digits then an "invalid string format" exception is thrown. I expected the invoice_number to be more free-form. Have I missed something or is this standard for the sandbox?
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