The issue is that each ModifyItemUses consumes one ServerAPI call, which leads to errors when player tries to modify uses to more than 15 items at once.
For example in my game there is a crafting mechanics, player starts to crafting multiple items, and when he comes back he should claim all of them at once so even upgrading the free tier won't help that much, ModifyItemUses to multiple instances in one request will solve the issue.
The request should have a array or dictionary of InstanceID and Value pairs, so it will be possible to modify a lot of items at once. Current method sucks, its too simple and you can't make complex inventory.