Notice the custom customer number is greyed out because Custom Customer # + Autogenerate is turned on in the settings. In this case, FollowUp will pick up the highest number on Foundation, increment it by one, and create a customer on Foundation, and enter that number here in the greyed out field. (If Custom Customer # is turned on without Autogenerate, then this field WILL NOT be greyed out, and you will need to enter a customer # here. If custom # is not turned on, then the Company ID from the URL will be sent as the customer # to Foundation, while creating customer)