Errors

The onError callback includes an errorCode and errorMessage. The various error scenarios are described below.

`errorCode`	`errorMessage`	Description
`Session_Not_Found`	Session not found	A session was not found when initializing the SDK.
`Session_Expired`	The session is expired	The session being used in the SDK expired.
`Client_ID_Not_Found`	Client ID not found	The SDK could not determine the `client_id`.
`Internal_Error`	Internal error	An internal error occurred.
`Merchant_ID_Not_Found`	Merchant ID not found	The merchant ID is required when product type = transaction_link.