I'm finding difficult in finding out the U.S sourced Income. Our vendor operate from Germany, but all the services are performed in the Cloud. Now, How can I determine whether it is U.S Sourced Income, which is reportable to IRS. Please help me out.

UNLESS your vendor is physically presented in US or his work was done in US(either of the htese or both of these), your vendor doesn't need to submit you W8BEN;however, if you want hom to submit the form to you , then he may do that as there is no penalty in submittng the form to you.A nonresident alien (NRA) usually is subject to U.S. income tax only on U.S. source income;his personal income earned inside the US. As with most other countries, U.S. source income is taxable in the US.