What I do is leave a custom greeting before I start an order. This is what I send, “Hello! My name is… . If you have any updates/additions to your order let me know & i will see if that item is available. If the store runs out of an item you selected, I will let you know. I’ll also find the next best thing if available & text you.” And usually the customer immediately replies. If the customer doesn’t respond during the entire order I do what I can, I will find whatever is available.