Financial activities, such as the exchange of money between individuals, have long been considered a crucial aspect of how people build and maintain their interpersonal relationships (i.e., a strong, deep, or close association/acquaintance between two or more people) with individuals they know because money is a sensitive social construct. In particular, over the past decade, how to conduct, manage, and experience money exchanges and processes between individuals has been dramatically transformed due to the increasing popularity of digital peer-to-peer (P2P) payment services (i.e., performing one to one online money transactions via a digital device). In this sense, digital P2P payments have shown the potential to affect how people pay and interact with each other regarding money, an important impact factor on various forms of interpersonal relationships, by facilitating direct money transactions between individuals through computer-mediated channels. Therefore, this dissertation research is motivated to leverage a sociotechnical approach to conduct an in-depth investigation of the nuanced human experiences of personal money exchanges mediated by digital P2P payments between people who know each other and the unique role of digital P2P payments in shaping these individuals' social connections with each other online and offline. In doing so, this dissertation research aims to (i) reveal and elaborate the multidimensional influences of digital P2P payments on interpersonal relationships between people who already know each other in terms of both experiences of money exchanges and everyday social interactions; ii) advance our knowledge and understanding of how digital P2P payments systems can be redesigned to better support people's social connections with individuals they know; and iii) envision the future landscape of digital P2P payments in our increasingly networked digital society. This dissertation research involves four studies. Grounded in 158 social media posts and 8 interviews, Study 1 explores how people perceive the increasing trend of integrating digital P2P payments with social media services (e.g., Facebook Messenger payment) and why they decide not to use this service in their daily lives. Study 2 reports findings of a qualitative study of 31 in-depth semi-structured interviews to investigate the influences of using digital P2P payments on people's offline interpersonal relationships. Study 3 reports results of a large-scale anonymous online survey with 218 valid responses to measure the specific immediate social consequences and lasting impacts of using digital P2P payments on people's interpersonal relationships. Study 4 adopts the research through design (RtD) approach with a specific emphasis on participatory design activities to both elicit and qualitatively investigate user needs and user-generated design solutions for digital P2P payment services that can better support people's social connections. This dissertation research thus contributes to innovating financial technologies in the perspective of Human-Computer Interaction and Human-Centered Computing by better understanding new and more complicated social phenomena and dynamics emerging in today's digital economy. First, this dissertation research offers one of the first empirical evidence to unpack and explicate the multidimensional influences of digital P2P payments on both financial experiences/processes and everyday social connections between known contacts, which is understudied in prior scholarship. In doing so, we provide new perspectives on today's technology-mediated financial life and shed light on the intertwining financial and social relationships through technology. These insights also help re-conceptualize computer-mediated interpersonal relationships in today's networked society. Second, we identify and further reflect on user-generated design recommendations and develop prototypes that highlight the importance of taking the interplay of financial and social engagement, in addition to security and privacy, into consideration when redesigning digital P2P payments platforms. Through this RtD approach, we thus rethink and envision the future landscape of digital P2P payments where such technologies can be designed, developed, and used in a more comfortable, innovative, and emotionally satisfactory way. As we are entering a post COVID-19 pandemic age, there is an increasing interest to make digital financial technologies not only secure but also more human-centered, interaction-centric, and culturally sensitive, which can be used to better support and maintain human connections through daily financial activities with or without face-to-face interaction. Therefore, in a broader sense, this dissertation research on the social values of digital P2P payments also contributes to building a more robust and inclusive digital economy in today's changing society.