By default when you change the inventory of an out-of-stock product to 1, notifications will be sent to your customers. But for many reasons, you may need to set this number to something else. you can do this by navigating through your Restockify panel > Notify Channels> Advanced > Notifying subscriber.
Your "Notify me" emails will not be sent until your stock reaches your chosen number.
Different minimum inventory for products
Here comes the cool part. you can set different minimum inventories for different products. some products are in high demand and you need to send a notification when the inventory has reached 100 but some are different and you need to send notifications even if you have 1 stock. this is where this feature comes into play.
you can set different minimum inventories by tagging your Shopify products with the tag Restockify-min-inventory-X which X is the minimum number. for instance if you want a product minimum inventory to be set as 20 you should go to your Shopify admin and tag the product with the tag min-restock-inventory-20.