When a visitor leaves an email on the newsletter popup, the app’s contact status is updated to Subscribed.
However, if he checks out but does not choose to receive marketing emails on the checkout page, Shopify’s contact status is Not Subscribed.
The contact status from Shopify is synced back to the app.
This does not impact your email deliverability.
You can send the subscribe confirmation email by going to App Dashboard > Audiences > Contacts > Click on the contact > Hit on the Subscribe button.
In our Pro plan, the Sync contacts back to the Shopify function can prevent this case.