This study explores the acceptance of by.U, a fully digital prepaid service launched by Telkomsel in Indonesia. Despite being designed for Gen Z, internal data shows a significant portion of users come from older generations, revealing a gap between market expectations and reality. To analyze this phenomenon, the study integrates the Technology Acceptance Model (TAM) and the Diffusion of Innovation (DOI) theory to examine key factors influencing digital service adoption with several modification from studies earlier. Using a structured questionnaire, data were collected from 400 active by.U users who was born between 1997 and 2012. The analysis was conducted using Structural Equation Modeling with the Partial Least Squares (SEM-PLS) method. The results indicate that Attitude towards Using significantly influences Usage Behavior, with Hedonic Motivation, Compatibility, and Perceived Ease of Use as strong predictors of user attitude. Surprisingly, Perceived Usefulness had no significant effect, while Complexity showed a positive influence, contrary to theoretical expectations. These findings suggest that Gen Z’s technology adoption is driven more by experiential and emotional factors than by pure functionality. For digital service providers like Telkomsel, this highlights the importance of user-centric design focused on enjoyment, customization, and ease of use. This study contributes to the refinement of TAM-DOI frameworks for younger, digitally-native populations and provides practical insights for enhancing engagement in competitive digital service markets.