What does "subject to limited income tax liability" mean?

What does "subject to limited income tax liability" mean?

Pursuant to Art. 50 of the German Income Tax Act, GVL must deduct a reduced tax rate of 15% plus 5.5% solidarity tax from all amounts to be paid out to artists living abroad. If you want to avoid being subject to such a tax deduction, we need you to send us the exemption certificate issued by the Federal Central Tax Office.