Pop up help from old website to new

Hi @RoseLane, welcome to the community with your first post!

So a few things that can be happening here:

1. Shopify Theme Popups: For some Shopify Themes, they have a built-in popup feature as part of the Theme.  You can sometimes find it in the Theme editor.  But because this various a lot from one theme to another, it is entirely up to the Theme developer/publisher to include that as part of their Theme.
2. 3rd Party Popups: Are you using a third party popup tool? If so, you may need to migrate the integration code or app to your new theme.  
3. Enabled Klaviyo App Embed in Shopify: If you are using Klaviyo Signup Forms, and switched to a new Theme, make sure the Klaviyo App Embed is enabled.  You can follow the instructions here: How to enable onsite tracking for Shopify : Enabling the Klaviyo app embed in Shopify   

If you were using your previous Shopify Theme’s built-in popup feature, I recommend you use the Klaviyo Signup Forms instead.  Not only will you be able to quickly build Popups (and other email capture forms like Fly-outs, Embeds, and Full Screen Email Captures), it also lets you do advance targeting options, multi-step forms, and A/B testing and much more!  

Hope this helps, and let me know!

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Joseph Hsieh // retentioncommerce.com // twitter: @retenion