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Hi @henryouyang,

Thank you for sharing your question with the Klaviyo Community. Also, thank you @forman for your reply. 

When filling a Klaviyo sign-up form, the profile will not automatically be created in Shopify. Only if the user fills a Shopify form will they be added to the Shopify. Therefore, if you want profiles who sign-up to be included in both Shopify and Klaviyo, you must use a Shopify sign-up form. New newsletter subscribers are synced in real time through your Shopify integration to Klaviyo when they fill the form. They will simply have to confirm their subscription before being added to the Klaviyo list.

Thanks and have a great day.