Contract number: [ complete ]  Service contract conditions of December 2018  If no observations have been submitted or if  despite the observations submitted  the  contracting authority decides to pursue the recovery procedure  it must confirm recovery by  formally notifying a debit note to the contractor  specifying the date of payment. The  contractor must pay in accordance with the provisions specified in the debit note.  If the contractor does not pay by the due date  the contracting authority may  after informing  the contractor in writing  recover the amounts due:  If the contractor does not honour the obligation to pay the amount due by the date set by the  contracting authority in the debit note  the amount due bears interest at the rate indicated in  Article II.21.8. Interest on late payments will cover the period starting on the day after the due  date for payment and ending on the date when the contracting authority receives the full  amount owed. Any partial payment is first entered against charges and interest on late payment and then  against the principal amount.  If the contract is signed by a group (joint tender)  the group is jointly and severally liable  under the conditions set out in Article II.6 (liability). The contracting authority shall send the  debit note first to the leader of the group. If the leader does not pay by the due date the whole amount  and if the amount due cannot be  offset or can only be offset partially in accordance with Article II.23.2 (a)  then the  contracting authority may claim the amount still due to any other member or members of the  group by respectively  notifying  them with a debit note in conformity with the provisions laid  down in Article II.23.2. Such checks and audits may be initiated at any moment during the  performance of the  contract  and up to five years starting from the payment of the balance. The audit procedure is initiated on the date of receipt of the relevant letter sent by the  contracting authority. Audits are carried out on a confidential basis.  II.24.1  The contracting authority and the European Anti-Fraud Office may check or require an  audit on the  performance of the contract . This may be carried out either by OLAF’s  own staff or by any outside body authorised to do so on its behalf. (c) by taking legal action. (b) by calling in a financial guarantee if the contractor has submitted one to the  contracting authority; (a) by offsetting them against any amounts owed to the contractor by the Union or by the  European Atomic Energy Community or by an executive agency when it implements  the Union budget; II.23.3. Interest on late payment  II.23.4. Recovery rules in the case of joint tender  II.24. CHECKS AND AUDITS  37 