I am designing an online service that serves employees of customer of my customers. End users in this system are employees of customer of my customer.
And my customers are mostly organizations, not individuals.
How to call organization that is customer of my customer? How to call employees of that organization?
UPDATE: I also provide an Application Programming Interface for my customers to work with their customers. So, I need to describe end users in the way that my customers (its developers) understand well. Also, there are several types of end users of this software. For instance, another type is members of support team of my customer organization.