USPTO Certification Fee. An international application must include the USPTO certification fee for each class of goods/services for which international registration is sought, or it will not be certified. The certification fee per class increases if the international application is based on more than one basic application or registration. 37 C.F.R. §§7.6(a) and 7.11(a)(9).
International Fees. If an international application is submitted through TEAS, the international fees for all classes and all designated Contracting Parties must be paid at the time of submission. 37 C.F.R. §7.11(a)(10). International fees for paper applications must be paid directly to the IB, and may be paid either before or after the international application is submitted to the USPTO. 37 C.F.R. §7.7(c). However, international fees paid after the IB receives the international application could result in a notice of irregularity issued by the IB ( see TMEP §1902.07(b)(i)).
See also TMEP §1903.02 regarding payment of international fees.