Enter your Street Address (and not a P.O. Box) in the Street Address 1 field.
The Street Address field is a "required" field. Information must be entered in the field in order for the page to be saved. If you fail to enter valid information in a required field, a popup error message is displayed when you click Next.
Please indicate your preferred address for all of the address-related fields as this address will be used for payment purposes and for receipt of proper tax documents, i.e. 1099 form.