You can use this request to create many contacts at once. This request is similar to the Create Contacts in Bulk method, but it runs the contact creation asynchronously.
Once you make the request, we will store the data you have sent and immediately give you a response saying that the data is stored. Then the data will be processed on our side without you having to wait for it to be done within the scope of the API request. Because of this, it should allow for a lot more contacts to be sent at once, whereas bulk create is limited to 2,000 at a time.