With the aim to develop e-commerce and achieve the government's goal of cashless transactions in Vietnam, the adaptation of online payments by people is compulsory. However, it is reported that a large proportion of middle-aged consumers in both urban and rural areas are unfamiliar and not ready to access online payment forms. The study utilises qualitative and quantitative analysis methods to test the research hypotheses. By surveying 295 middle-aged consumers working in various businesses, political and social organizations, and government agencies, the research has revealed that there are 3 groups of factors affecting the decision to use online payment of middle-aged consumers, including consumer trust, subjective norms, and perceived behavioural control - in which the trust of middle-aged consumers is also influenced by the perceived usefulness of online payments. Last but not least, the paper has proposed a number of issues to help businesses and payment service providers develop specific solutions to promote consumer behaviour and online payment of this large group of potential customers.