You can connect ReStock Alerts to your Shopify contact list in order to have the customers that have requested to be notified when back in stock in your Shopify customers lists.
to have this feature, you need to activate it in Account Settings> Integration> Shopify contact.
Click on the Connect button.
To add customers to your Shopify you should give ReStock Alerts access to it. when you click on the connect button you'll see a pop-up telling you what you need to do.
Click on the Shopify contact access button and you will be redirected to the below page:
Click on the Update app button to update the app's access.
Following that, you will be taken to the home page of ReStock Alerts. please head back to the Settings> Integration page and click on the connect button for Shopify contact.
Check the Configuration box and click on the Save button.
And that's it. you will now have your customers that have registered for restock email in your Shopify admin> Customers.
