Hi,
You have an awesome product and the potential is right here! 
However as a developer who is working with your API, It really lacks the ability to bulk upload new Orders, Abandoned carts, Custom fields and other DeepData operations since store owners have a lot of data they need to push over and without Bulk option, it takes a lot of requests and it is very slow and inefficient at the moment.
As an example, it is really not optimal to be sending 3 separate requests if I have 3 custom fields that I must update for a given customer / contact. All of this should go in one request to save resources and speed.
This is a very important feature and it will improve the life for all users and devs
MailChimp API at the moment is a lot more efficient, but you have a lot better user interface and automation building, contact management etc. So overall you have an excellent product, but we need to fix this API process
Please add this to your API.