Back In Stock,Notify Me: Kbite

The app is straight forward--easy to navigate and when I hit a little hiccup, the customer service was quick to reply and help me fix it quickly. It's definitely worth downloading and trying out. Their FREE option does what you need it to with options to pay (a reasonable price tbh) to grow its capabilities along with the growth of your store. I'm happy with it--recommend to anyone looking for a "notify me when back in stock" button that will automatically populate when you're sold out and notify you.
Clean, easy, and good customer service, what more can you want?