The single flat-rate technical assistance operation, established pursuant to Delegated Regulation (EU) 2019/1867, which entered into force on 09 November 2019, corresponds to the programming of technical assistance expenditure, declared on a flat-rate basis to the European Commission. The REACT-EU initiative that supports the ERDF-ESF Operational Programme presents a challenge for the Managing Authority: select and pay for new operations in less than 3 years, while successfully completing the management of the initial appropriations and the closure of the programme. The mobilisation of technical assistance credits is a major means of success of this challenge.