UX for Android PAX, Ingenico, and Sunmi Terminals

Design Challenges and How We Solved Them

Designing payment terminal interfaces is fundamentally different from mobile app design. The UX constraints are unique to this domain, and getting them wrong has real-world financial consequences.

Designing Across Screen Sizes and Form Factors

The 16+ terminals in this project range from a 3.5″ PinPad screen (PAX A35) to a 10″ desktop display (Sunmi P3 Mix). Every UI element — buttons, typography, icons, animations — had to scale gracefully across this entire spectrum while remaining fully functional and legible.

Merchant vs. Cardholder UX

This is the iconic challenge of payment terminal design. Many screens serve a shared merchant + cardholder experience — the merchant initiates a sale, then hands the device to the cardholder for PIN entry or contactless tap. The UX needs to be immediately intuitive to cardholders who interact with these devices rarely and don't hold them close to their face. UI elements must be high-contrast, large enough to read from a distance, and self-explaining.

For unattended self-service terminals (petrol stations, vending machines, parking), the challenge intensifies — there is no merchant to guide the cardholder through the flow. The entire experience must be self-explanatory, with clear visual cues for card insertion, NFC tap zones, and transaction progress.

EAA 2025 and WCAG 2.2 Accessibility

The current release is fully compliant with the European Accessibility Act (EAA) 2025 requirements and meets WCAG 2.2 at AA level. Our accessibility implementation includes:

1. APCA-compliant contrast ratios — We use the Advanced Perceptual Contrast Algorithm (APCA) rather than just WCAG's legacy contrast formula, ensuring that text and interactive elements are perceptually distinguishable in real-world viewing conditions — including bright outdoor environments and low-light retail settings.
2. 132×132px minimum touch targets — Exceeding WCAG's 44×44px recommendation, our touch targets are sized for the reality of payment terminals: gloved hands, hurried transactions, and users who may have motor impairments.
3. VoiceOver toggle — The interface supports screen reader technology, allowing visually impaired users to complete transactions independently.
4. Accessible color palette — Designed so that critical transaction states (approved, rejected, pending) remain distinguishable for users with all types of color vision deficiency.

PCI/EMV LED Indicator Integration

PCI and EMV certification require 4 physical LED indicators on the terminal. Our challenge was to integrate these LEDs into the UI so they feel native to the design — not like an afterthought bolted on for compliance. We positioned the LED indicator at the bottom of the screen, where it connects perceptually with the 2-decade legacy of these indicator lights that users subconsciously recognize, while staying clear of the NFC reader area so it doesn't get covered when users tap their card.

Custom Icons & Splash

Each item on the Menu list was enriched with a dedicated custom icon.
To make things look even more custom, we have designed the app's Splash Animation and Launcher Icon

Custom Vector Animations

All animations in the UI are Vector-Based (super-crisp):

1. Ways to use the card (video below)
2. Transaction-Results (Accepted, Rejected)
3. Question mark that appears when there is some decision to make
4. Spinner that appears at times of processing, connecting, etc.

Transaction Result Screens

It is challenging how to deal with the transaction rejection with delicacy. Our main challenges were:

The transaction result is the most critical moment of the entire payment experience. The accepted and rejected states need to be instantly distinguishable — even from a distance, even in bright sunlight, even for users with color vision deficiency. Our client reported real-world cases where merchants missed rejected transactions because the screen lacked sufficient contrast. We designed a high-contrast rejection screen that is unmistakable — bold, legible, yet not alarming to the cardholder standing nearby. Balancing delicacy with visibility required careful iteration.

Why we've made Rejection Screen red❓
Piotr Wilk (our UX Lead) has talked about it with Stéphane Joseph, on his "Think, Act, Lead" podcasting series.

Light Mode / Dark Mode

Payment terminals operate in every environment — from sunlit outdoor terraces to dimly lit restaurant dining rooms. We designed both a Light Mode for bright environments and a Dark Mode for low-light settings, ensuring optimal readability and reduced eye strain for merchants who process hundreds of transactions per shift.

Is the Client happy?

Michał Sodel / Product Manager @ eService | GlobalPayments

[Translated from Polish] I highly recommend working with Piotr and the TeddyGraphics' team. We had the opportunity to collaborate on several complex UX projects related to payment applications—both mobile and running on payment terminals—and it was a very strong, partnership-based collaboration.

One of our joint initiatives included UX Writing for the eService Tom application, where we worked directly on XML files, translating and adapting the app’s navigation into Polish in line with UX writing principles used in eService payment applications, which we have been responsible for since 2017. Piotr’s experience in fintech projects was instrumental in delivering this scope with high quality, consistency, and alignment with industry best practices.

Another major area of our cooperation was a comprehensive UX/UI redesign of the entire eService payment application across all supported terminals (including PAX, Ingenico, and Sunmi) to meet the requirements of the European Accessibility Act 2025. This was an extensive and demanding project, involving multiple devices and hardware constraints, and Piotr with his team navigated this complexity very effectively.

Beyond his professional expertise, Piotr is an excellent collaborator—highly communicative, responsive, available, and open to feedback. He demonstrated creativity, deep domain knowledge, and strong attention to detail. I truly enjoyed working with him and confidently recommend him for UX projects, especially in the area of payment and fintech products.