I read the document again, A string of 64 or fewer UTF-8 characters containing the canonical name for your store, suitable for display. This needs to remain a consistent value for the store and shouldn’t contain dynamic values such as incrementing order numbers. Don’t localize the name. Use only characters from the supported character sets in the fonts listed in the table below. ref : Request Parameters how we are invoking the completeMerchantValidation() session.completeMerchantValidation({ displayName: 'じゃ', //utf-8 string //... other params from the docs }) Can you please help to understand if it adheres to use canonical name. don't localize.. Note: if the displayName is in english, it works.