One way to determine customers for service design is to imagine a wall around the business. Everything inside the wall is the people and processes that are part of the company. Everything outside the wall is not part of the company. This means that the outcome of a service is also outside of the company.
The wall is the company and its processes
When customers are identified they are outside of the company, they are outside of that wall.
Everything the company does is because of some outside influence. There should be nothing in a company that exists just because the company exists.
Accounting is done because the government is requesting the tax submission. The government is the customer and the outcome is the tax forms.