Hi there, yosserbusiness.

QuickBooks Online requires a U.S. address when you add a new employee. If the employee is working in Spain, the option is unavailable because of the tax requirements.

If your employee is a nonresident working in the United States, you can check these articles for more information:

• Exemption status of foreign employees with particular visa types
• Set up Nonresident Alien (NRA) tax withholding for foreign employee

If you need more help with QuickBooks Online Payroll, feel free to leave a comment. Thanks.