Can't certify to the W8 form

I have provided all the necessary data and the W8 form was generated for my account.

Despite that, the button “I certify” is not available for me. How can I certify to the W8 form?

I am self-employed and work as a contractor to various IT firms. When I was asked about my employement status, I chose the “unemployement” option. Can it be the reason why I can’t sign the W8 form?