Performance guarantees cover compliance with substantial contractual obligations until the  contracting authority has given its final approval for the service. The performance guarantee must not  exceed 10 % of the total price of the contract. The contracting authority must release the guarantee  fully after final approval of the service, as provided for in the contract. Retention money guarantees cover full delivery of the service in accordance with the contract including  during the contract liability period and until its final approval by the contracting authority. The  retention money guarantee must not exceed 10 % of the total price of the contract. The contracting  authority must release the guarantee after the expiry of the contract liability period as provided for in  the contract.  The contracting authority must not request a retention money guarantee where it has requested a  performance guarantee. The contractor (or leader in the case of a joint tender) must send an invoice for interim payment, as  provided for in Article I.5 or in the tender specifications. The contractor (or leader in the case of a joint tender) must send an invoice for payment of the balance  within 60 days of the end of the period of provision of the services, as provided for in Article I.5 or in  the tender specifications. Payment of the invoice and approval of documents does not imply recognition of the regularity,  authenticity, completeness and correctness of the declarations and information they contain. Payment of the balance may take the form of recovery. The contracting authority may suspend the payment periods specified in Article I.5 at any time by  notifying  the contractor (or leader in the case of a joint tender) that its invoice cannot be processed.  The reasons the contracting authority may cite for not being able to process an invoice are:  The contracting authority must  notify  the contractor (or leader in the case of joint tender) as soon as  possible of any such suspension, giving the reasons for it. In cases b) and c) referred above, the  contracting authority shall notify the contractor (or leader in case of a joint tender) the time limits to  submit additional information or corrections or a new version of the documents or deliverables if the  contracting authority requires it. Suspension takes effect on the date the contracting authority sends the  notification . The remaining  payment period resumes from the date on which the requested information or revised documents are  received or the necessary further verification, including on-the-spot checks, is carried out. Where the  suspension period exceeds two months, the contractor (or leader in the case of a joint tender) may  request the contracting authority to justify the continued suspension. Where the payment periods have been suspended following rejection of a document referred to in the  first paragraph of this Article and the new document produced is also rejected, the contracting  authority reserves the right to terminate the contract in accordance with Article II.18.1(c) . On expiry of the payment periods specified in Article I.5, the contractor (or leader in the case of a  joint tender) is entitled to interest on late payment at the rate applied by the European Central Bank  for its main refinancing operations in euros (the reference rate) plus eight points. The reference rate  32  II.21.8. Interest on late payment  II.21.7. Suspension of the time allowed for payment  II.21.6. Interim payments and payment of the balance  (a) because it does not comply with the contract; (b) because the contractor has not produced the appropriate documents or deliverables; or (c) because the contracting authority has observations on the documents or deliverables  submitted with the invoice.