The challenge
Build a mobile payment solution that lets small vendors and informal businesses across Brazil accept contactless payments using only their phone — no terminal hardware required. This was iti's proximity selling product, the first of its kind targeting individual users in the country.
The audience made the design challenge specific: many of these vendors had limited experience with digital technology. A payment app that assumed smartphone fluency wouldn't work. Every interaction had to be self-explanatory.
Approach
We started with the core user flow: receiving a payment. The original design relied on text prompts and multi-step confirmations. Usability tests revealed that users responded better to visual cues than written instructions — icons and contextual graphics reduced errors and completion time.
Key design decisions:
We used SUM (Single Usability Metric) analysis to measure improvements across iterations — tracking task completion rate, time-on-task, and error frequency together rather than in isolation.
Turning point
The breakthrough came when usability metrics showed a clear jump in independent transaction completion. Users who had struggled with earlier versions could now process payments confidently without assistance.
Two findings shaped the final design:
Outcome
The app launched with positive reception from vendors, who valued its simplicity. The project demonstrated that accessible digital finance tools don't require dumbing down the technology — they require removing unnecessary friction between the user and their goal.
The core constraint: designing for users who can't afford to make a payment mistake, in transactions that happen face-to-face with a customer waiting. That pressure shaped every screen.