Enter additional address information (such as a suite number, floor number, building name, or P.O. Box) in the Street Address 2 field.
The Street Address 2 field is not a "required" field. You are not required to enter any information in this field in order to save the other information you enter on the page.
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.