Update godoc and error message
Update godoc and error message

WPTechInnovation/worldpay-within-sdk,WPTechInnovation/worldpay-within-sdk,WPTechInnovation/worldpay-within-sdk,WPTechInnovation/worldpay-within-sdk,WPTechInnovation/worldpay-within-sdk,WPTechInnovation/worldpay-within-sdk