Case 02 · Crypto payments · iOS app · 0 → 1
Crypex lets people in Brazil pay a Pix straight from their crypto balance, without selling, withdrawing and waiting first. I designed it from a blank file to a dev-ready handoff in about six weeks, as the only designer, side by side with the engineer who founded it.
Cryptocurrencies as conventional payment methods
Overview
The founder, a software engineer, wanted to see a simple idea take shape: treat cryptocurrencies as a conventional payment method. Hold ETH, BTC or USDT, and use that balance to pay a Pix, the instant payment most Brazilians already use every day, without ever leaving the app.
There was no earlier version to fix. The brief was the product itself: the flows, the interface and a small set of components a developer could build from. All of the UX and UI in the file is mine, from the first drafts and the splash screen to the handoff, shaped in close, direct conversation with the founder.
The challenge
Paying a bill with crypto usually means selling on an exchange, withdrawing to a bank account, waiting for the transfer and only then paying. Every hop adds a fee, a delay and one more chance to make a mistake with money that can't be pulled back.
How might we
make paying with crypto feel as ordinary, and as safe, as paying with Pix?
Constraints
Orange was the founder's colour and not up for debate. The system had to be built around it.
Crypto quotes move by the minute, so reais and crypto can drift apart in the middle of a payment.
A transfer on the blockchain can't be reversed. Every step before confirming has to leave room to check.
About six weeks, one designer and one engineer. Every idea had to be cheap to test.
Process
A freelance timeline has no room for interviews and personas. So I leaned on what we did have: a founder who knew the domain, a developer who could put screens on localhost within days, and five people willing to try them.
Pin down the one job with the founder: pay a Pix using a crypto balance.
Sketch the pay flow screen by screen, then sign-in and home around it.
Try the flows on a localhost build with 5 people: developers and people new to crypto.
Rebuild the pay flow around what worked, then add every state and error.
Components and sections marked ready for dev, for the founder to build from.
Redrawn for this case study from the final screens.
First draft · 6 screens
Final · 3 steps
The drafts asked for the amount in reais and only later for the currency to pay with, so people saw what they were really spending at the very end. Folding both into a single converter put the trade in plain sight and cut the path from six screens to three steps. On the localhost build, it was the version that worked best for both groups, developers and people new to crypto.
Notes from the localhost build, and what each one changed.
We saw
People typed an amount in reais and only met the crypto side on the last screen. Some went back to change the value once they saw it in ETH.
So I
Put both sides of the trade on one screen, with the live rate right under them.
We saw
People new to crypto compared it with the Pix in their bank app, which they finish in seconds. Six screens felt like filling in a form, not paying.
So I
Merged six questions into three steps: amount, recipient, review.
We saw
With the phone keyboard open, the other currency and the rate slid out of view while people typed.
So I
Designed a built-in keypad that leaves both values and the rate on screen.
We saw
Before tapping continue, people looked for the recipient's name, the habit their bank app has taught them.
So I
Show name, masked CPF and bank as soon as the Pix key goes in, before anything is sent.
We saw
Developers asked what happens if the price moves while the transfer is pending. Everyone else asked about the fee.
So I
Locked the quote for ten minutes with a visible countdown, and listed the fee and both totals, reais and ETH, in plain view.
The solution
Pay · amount
Pay · recipient and review
Pay · endings
With money on the line, the last screen matters as much as the first. Success and failure share one calm layout: a single symbol, one sentence in plain words and one way forward, straight to the payment history.
Home
Payment history
A running total for the period, the number of transactions and a search by name or code. The period opens a calendar for any range, with a year picker for going further back.
Sign-up and sign-in
Orange came with the brief. Rather than fight it, I built the whole system to make it earn its place. It's the colour people already link to Bitcoin, and it's warm in a market that usually dresses in cold black and blue.
To keep it from shouting, everything else stays calm: soft greys, white cards and near-black type. Orange is saved for what matters: the main button, the active tab and the one number worth checking twice, the total. Green and red appear only for results and market moves.
One thing I'd change
White on this orange reaches 3.05:1. WCAG accepts that for large text, 14 pt bold or 18 pt regular, but not for a 16 pt regular label. So the fix is typographic, not chromatic: same orange, same white, with the label set at 19 pt bold. It passes, and the main action reads with more confidence.
Every screen is built from these parts.
Each state lives as a variant in Figma, so the build never depends on guesswork. The bell turns orange when there's something new, the tab bar has one state per tab, and the main action works both on the page and on a sheet. Service cards carry a badge for what's new or coming soon, so the roadmap shows up in the app itself.
Navigation
Actions
Inputs
Cards and lists
Pickers
Feedback
Logo, app icon and splash, all part of the file.
Outcome
The founder wanted to see how the product would look and feel before committing to it, and the file answered that. It was handed off complete: sign-up and sign-in, home, the Pix flow with all of its states, payment history and a small component set, in sections marked ready for dev.
Launch was put on hold by Brazilian bureaucracy. At the time, the rules for crypto service providers were still being written: the Central Bank became the sector's regulator in 2023, and its authorisation rules only came out in November 2025. The project is paused, not dropped, and I'm still the founder's designer for when it picks up again.
When it picks up again
The next flows, boleto and card, go through the same five-person loop before they reach the file as final.
Working on something similar? Tell me about the product, the feature or the messy flow.