A fee that has been validly paid (see A-X, 7.1.1) is not refunded. For instance, a validly paid further processing fee is not refunded if the request for further processing is rejected due to non-completion of the omitted act, which is another requirement of Rule 135(1) (see E-VIII, 2). As an exception to this general principle, a validly paid fee is refunded if there are special provisions for the refund in either the EPC or the Rules relating to Fees (see A-X, 2).
By contrast, any fee which has not been validly paid is to be refunded. See subsections A-X, 10.1.1, to A-X, 10.1.3, below.
Source: http://www.epo.org/law-practice/legal-texts/html/guidelines/e/a_x_10_1.htm
Date retrieved: 17 May 2021