Hi @Lauren SC, 

Welcome to the Community! Thanks for sharing your question with us. Sorry you’ve experienced that inconvenience and I can understand how frustrating it might have been. Would love to help give some insight into what might’ve happened here. 

When you noticed that users aren’t being synced to the correct list form your integration’s website, it’s a good idea to investigate whether the right list is chosen to receive these new subscribers in your integration’s tab . Does the list you’ve chosen in your integration tab match the list you’ve linked to your Welcome Flow? 

If your Newsletter List is connected to your Welcome Flow, then tagging them in Shopify would cause them to go through the Flow, if they had not gone through it before, no matter when they were originally subscribed. This is because they set off the trigger of the Flow for the first time: being added to the ‘Newsletter list’.

It should also be noted that  a user cannot go through a List-triggered Flow twice, only once. So you can be assured that once a user that has gone through this Flow they will not again and not repeat this experience. 

I know how vast and confusing the product might be at first, but I have full confidence you will soon get the hang of it more by utilizing our resources such as our Help Center, Academy and Community more! I’d recommend checking out this Community post about syncing lists to a flow and these Academy course to increase on your product knowledge! 

• Getting Started with Klaviyo 
• Automating the Customer Journey with Flows

Thanks for being a part of the Community! 

-Taylor