First if you have never had an S-corp before I highly recommend you seek local professional guidance to be educated in the filing & payroll requirements and bookkeeping aspects so you start off on the right foot ... getting it wrong will be painful later.
Next ... paying for services from a company requires you to have substantiation ... they should send you a receipt/invoice and you probably should have a contract on file. If withholding is required depends on many factors ... again seek local assistance with someone versed in international business.
