In general - you woudl need to collect a signed form BEFORE you make a payment.
That is because as a payer - you are treated as a withholding agent - and that is your responsibility to determine if withholding required.
That determination is made at the time of payment - so - I suggest to have all documents in perfect order before the payment is made.
Please also be aware that there is a tax treaty in effect between the US and
specifically - see page 19 - ARTICLE 15 Independent Personal
(1) Income derived by an individual
who is a resident of one of the Contracting States
from the performance of personal services in an independent capacity may be taxed by, that Contracting State. Except as provided in paragraph (2), such income shall be exempt
from tax by the other Contracting State.
(2) Income derived by an individual who is a resident of one of the Contracting States from the performance of personal services in an independent capacity in the other Contracting State
may be taxed by that other Contracting State, if:
(a) He has a fixed base regularly available to him in the other Contracting State for the purpose of performing his activities; in that case, only so much of the income as is attributable to that fixed base may be taxed in that other Contracting State;
(b) He is present in that other Contracting State for a period or periods
aggregating 90 days or more in the taxable year; or
(c) The gross remuneration derived in the taxable year from residents of that other Contracting State for the performance of such services in the other Contracting State exceeds 10,000 United States dollars or its equivalent in Philippine pesos or such higher amount as may be specified and agreed in letters exchanged between the competent authorities of the Contracting States.
Let me know if you need any help.