If the participant is funded for this project, then the participant will receive some payments for the provision of external services or the participant will also need to fill some timesheets to justify the personnel cost, or submit receipts/invoices for additional expenses for purchasing equipment or of other external services may needed?
The project does not ask for such proofs but since the Call follows the EU rules and conditions, beneficiaries should keep timesheets and receipts/invoices because EC could ask for them.