A deeper decarbonization perspective is undergoing with the increasing engagement of new distributed players and the deployment of innovative behind-the-meter flexibility services. Peer-to-Peer (P2P) trading has emerged as an innovative mechanism to foster the direct energy sharing among multi-level market players with pre-determined responsibility and privacy. However, compared with other P2P assets trading, P2P energy trading is facing huge challenges in achieving a large-scale commercialization due to the cooperation obstacles between non-professional distributed players and regulated players as Distributed System Operator (DSO), Transmission System Operator (TSO) and utilities. It is related to not only business and marketing, but also energy system operation to keep secure and reliable with injection of new roles, new utilization patterns, and new markets. This paper investigates the socio-technical interaction and mechanism for the sustainable P2P energy trading from the social dimension on the cooperation of multi-level market players, the technical dimension on the cutting-edge exchange of flexibility, and the economical dimension on the inter-operative decentralized/regulated marketplaces. Three questions are targeted on: (1) How Information and Communication Technology (ICT) enables co-creation of decentralized heterogeneous user-centered digital frameworks for the large-scale P2P trading interaction, (2) What specific energy services drive the cross-border interactions for exchange of multi-scale P2P flexibility, (3) How operational framework in P2P energy trading achieves the inter-operative marketplaces with the formation of trusted P2P energy society and the injection of multi-scale flexibility services. Finally, regulation challenges on P2P energy trading implementation are discussed for the guide of future work.