Objective: To analyze the adoption and use of the instant payment system, in parallel with informal installment sales, and its impact on the accounting and management of microentrepreneurs. Theoretical Framework: Microentrepreneurs face a major challenge in the business environment, which is the management of receipts. Since many of these do not occur at the time of sale, they use installment sales. Especially the informal ones, which in some places are called "fiado" or "pendura", as well as the "caderninho" (little notebook), alluding to the note for later payment. Method: The methodology involved a literature review covering PIX and its impact on informal commerce and business management. It also involved field research with microentrepreneurs and consumers using an electronic form. Results and Discussion: The findings highlight that the adoption of Pix has provided a more convenient and agile payment experience for consumers, especially in informal installment transactions. This has positively influenced consumer behavior, increasing the propensity to make installment purchases and generating greater loyalty. However, the implementation of PIX also presents challenges for microentrepreneurs, especially in terms of adapting accounting systems and financial management. The need to guarantee the security of transactions and comply with additional tax obligations is also highlighted as a concern for microentrepreneurs. Research Implications: This study has demonstrated that the adoption and use of PIX in informal installment sales has a significant impact on the accounting and management of microentrepreneurs, albeit with a limited scope of analysis. Originality/Value: These findings contribute to a more comprehensive understanding of the effects and encourage further research into this technological innovation in the contemporary business context.