If the transmittal fee, the international filing fee and the search fee are not paid within the prescribed time limits, or if the amounts paid are not sufficient to cover the fees due, the RO/EP invites the applicant to pay the missing amount together with a late payment fee for its own benefit (Form PCT/RO/133). Such payment has to be made within one month from the date of the invitation.
OJ EPO 1992, 383
The late payment fee is equal to 50% of the amount of the unpaid fee or, if the resulting amount is less than the transmittal fee, to an amount equal to the transmittal fee. The late payment fee may however not exceed the amount of 50% of the international filing fee as specified in the PCT Schedule of Fees (without taking into account any fee due for each page of the international application in excess of 30 pages).
If the applicant complies with the invitation (Form PCT/RO/133) within the indicated time limit, payment is deemed to have been made in due time.
If the applicant pays the fees after the time limit for payment expires but before the invitation is issued by the RO/EP (Form PCT/RO133), the payment is considered to have been received in time.
Nevertheless, if the applicant pays the fees after the time limit set in the invitation expires (Form PCT/RO/133) but before the RO/EP has despatched the notification of withdrawal of the international application (Form PCT/RO/117), the payment is considered to have been received in time and the application will not be considered withdrawn.