Q: Can I set up sku grid to email me when my FBA inventory has sold out? I just need a notification when my FBA items have sold out.
A: Yes, you can technically do this. You can create an entry in sku grid and use the link for the amazon item, tagged with your merchant id and the pricing option set to Only Offers Fulfilled by Amazon (#skuopt:fulfilled). You would not have to enter the marketplace or ASIN at the bottom of the add item form. You would just be using this url as the "supplier" URL. It's not a supplier, but that would be how you can get sku grid to track the stock of your FBA item.
so if your merchant ID is A123456789
and the ASIN for the item is B000112233
then your URL format for your URL would be https://www.amazon.com/dp/B001236578/?m=A123456789#skuopt:fulfilled
They will still follow the notification criteria from your notifications settings (unless you choose to manage them in a different sku grid account and then that way you can set it up to just notify you for stock changes).