Specifying Vendor ID

Our museum manager created a paid iBooks account and added me (using my Apple ID) as a group member. I want to submit a book via iTunes Producer. What do I put for the Vendor ID field? Is this ID something that the manager would have been given upon creating the account? Or is it assigned at the time of the first book's submission?

I want to ensure that the vendor ID is the one associated with the museum's account and not create a separate ID for me personally.