We performed a review of the legal regulation of the Ukrainian payment mechanism and the analysis of its modernization in the context of changing law enforcement in the financial (including payment) market under the influence of digitalization of public relations, in particular: we clarified the nature of legal relations in the payment services market, we studied the content and legal nature of payment services as a financial and legal category, we qualified the payment service as the basis of the legal payment mechanism. It is emphasized that the payment service in the legal dimension is a cross-sectoral phenomenon and is governed by civil, commercial, financial, banking, currency law, etc., and the activity of providing payment services by its legal nature has the features of both public (regulatory) and civil legal relations. It is concluded that the elements structuring the legal definition "payment service" indicate, that it is based on subjective and functional criteria, which, being combined in this legal structure, form the subject of payment service provider - performance/support of payment transactions. It is proposed to supplement the existing doctrinal classification of payment services according to certain additional criteria, which allow to characterize it as a system of interconnected elements (payment transactions) covered by the dialectic of whole and part, general and individual, according to certain criteria. Based on the legal analysis of the legal definition "payment service", its doctrinal definition is proposed, i.e., payment services are activities (independent or with the involvement of commercial agents) of public authorities, local governments, banks (according to the banking license) and legal entities (on the basis of a license for inclusion in the register) for the execution and/or maintenance of payment transactions using modern payment instruments on a contractual basis with the consumer of such services at the expense of own or borrowed from the provider with compliance with the requirements for their separation and preservation. The hypothesis of the structure of the legal payment mechanism new model is expressed, and the conclusion about the formation of a new paradigm of the payment mechanism and its legal regulation taking into account the digitalization of relations in the field of payment services is made. It is emphasized that the payment mechanism should focus on the consumer of payment services - protection of his rights and interests. Some directions of further research work on the legal mechanism of payments, payment market, payment services are identified.