26.5. The payments shall be made as follows:  a) 40% of the total contract price after the signing of the contract, against provision of  the performance guarantee and of a pre-financing guarantee for the full amount of  the pre-financing payment, unless otherwise provided for in the special conditions.  The pre-financing guarantee shall be provided to the contracting authority following  the procedure foreseen for the performance guarantee in accordance with Article  11.3-5, and in accordance with the format annexed to the contract. The pre-financing  guarantee must remain valid until it is released 30 days at the latest after the  provisional acceptance of the goods. Where the contractor is a public body, the  obligation for a pre-financing guarantee may be waived depending on a risk  assessment made;  b) 60% of the total contract price, as payment of the balance, after receipt by the  contracting authority of an invoice and of the application for the certificate of  provisional acceptance;  26.6. Where only part of the supplies has been delivered, the 60% payment due following  partial provisional acceptance shall be calculated on the value of the supplies which have  actually been accepted and the security shall be released accordingly.  26.7. For supplies not covered by a warranty period, the payments listed above shall be  aggregated. The conditions to which the payments of pre-financing and final payments  are subject, shall be as stated in the special conditions.  26.8. The payment obligations of the European Commission under this contract shall cease at  most 18 months after the end of the period of implementation of the tasks, unless the  contract is terminated in accordance with these general conditions. 26.9. Unless otherwise stipulated in the special conditions, the contract shall be at fixed prices,  which shall not be revised.  26.10. The contractor undertakes to repay any amounts paid in excess of the final amount due to  the contracting authority before the deadline indicated in the debit note which is 45 days  from the issuing of that note. Should the contractor fail to make repayment within the  above deadline, the contracting authority may (unless the contractor is a government  department or public body of a Member State of the European Union) increase the  amounts due by adding interest:   at the rediscount rate applied by the central bank of the country of the contracting  authority if payments are in the currency of that country;   at the rate applied by the European Central Bank to its main refinancing  transactions in euro, as published in the Official Journal of the European Union, C  series, where payments are in euro,  August 2020 c4e_annexigc_en  Page 22 of 36  on the first day of the month in which the time-limit expired, plus eight percentage points.  The default interest shall be incurred over the time which elapses between the date of the  payment deadline, and the date on which payment is actually made. Any partial payments  shall first cover the interest thus established.  Amounts to be repaid to the contracting authority may be offset against amounts of any  kind due to the contractor. This shall not affect the parties' right to agree on payment in  instalments. Bank charges arising from the repayment of amounts due to the contracting  authority shall be borne entirely by the contractor.