Hi there,
Welcome to the Community. I'll be happy to answer your question.
The Projects feature can only work with just one customer. I know how having multiple customers associated with a project can benefit you. I encourage you to send feedback about this to our engineers by clicking the gear icon and looking for Feedback. New product ideas and improvements are largely based on the feedback we get from users like you. For more info about Projects, check out the following articles:
Projects FAQ's
Set up and us the Projects Feature
Converting existing sub-customers into project
Let me know if you have questions.
