When does the fee for submitting an international application typically become due?

The fee for submitting an international application generally becomes due at the time of request submission. This aligns with the structure of the Patent Cooperation Treaty (PCT), under which international applications are filed. When an applicant submits an international application, they are required to pay the international filing fee simultaneously. This initial fee must be paid to initiate the processing of the application under the international phase of the PCT.

This requirement ensures that the application is considered valid and allows the International Searching Authority (ISA) to begin its examination process. The other options do not accurately reflect the timing of the fee obligation under PCT regulations. For instance, the fee isn't contingent upon the ISA's review or linked to a national application filing, nor can it be submitted late without risking the application's standing.