Hi @Sophie Bennett - Welcome to the community!

First, check your List called “Email Subscribers” to see if you have double-optin enabled.  If it is, then subscribers have to click on the email to confirm their subscription.  Once they confirm, they will start the flow. Also, verify that when users “sign up” they are going into your “Email Subscribers” List - since that is the List Subscription this Flow is triggered on.

Alternatively, you can also disable double-optin which skips the step that requires users’ to confirm.  For high volume subscribers, or sites that have a lot of “bot” or “fake” subscribers, you may not want to do this to keep your list quality high.

See here: 

Additional Klaviyo Documentation to Help:

• Guide to The Double Opt-In Process
• How to Verify That New Contacts Are Being Added to a List

Hello @Sophie Bennett,

Building off of @retention’s wonderful suggestion, can you let us know if the form you are using is a Klaviyo built form or one provided to you as part of your Shopify theme?

If the form was a provided to you as part of your theme, can you confirm if you’ve updated the form’s hidden input group tag with <input type="hidden" name="contact=tags]" value="newsletter"> and enabled Accepts Marketing in your Shopify integration settings? A refresher on how add this hidden input group tag can be found in the Sync Your Shopify Newsletter Subscribers to a Klaviyo List subsection of the How to Integrate with Shopify article.
 

I would also recommend taking a look at some similar Community posts, such as the ones below, to see if any of the solutions provided in them can help you resolve your issue as well

Hope this helps!

-David

I think most has been said above.

Check if people are getting on the list first

Then also check if your list is the same name as what you're triggering the flow on “Email Subscribers” If people are signing up on another list it won't trigger.

Another thing you can do to have a bit more visibility is to click the show analytics button in the top.