Following up on the discussion about smart wallets and onboarding in Treasury Committee 2026: BD + Marketing + Growth Wishlist - #27 by StacksArt — I wanted to share what we’ve learned exploring credit card onramps for Pillar and see if others have found better solutions.
Our Use Case
Pillar uses passkey-authenticated smart wallets. Users who don’t have crypto need a way to fund their wallet. Our ideal flow:
- User clicks “Buy with Card” in-app
- Embedded widget lets them purchase BTC with credit card
- BTC is sent to a taproot (bc1p) address generated via Emily API
- sBTC bridge automatically mints sBTC to their smart wallet
This isn’t a simple “buy STX to a Stacks address” flow — we need BTC sent to a custom Bitcoin L1 taproot address.
What Works Today (Mainnet)
We already have this working on mainnet:
- User opens “Deposit BTC” in Pillar
- We generate a taproot deposit address via Emily API linked to their smart wallet
- User buys BTC on Coinbase/Kraken/Cash App with credit card
- User withdraws BTC to the taproot address
- sBTC bridge mints sBTC to their smart wallet
This works. The UX gap is that users have to leave our app, go to an exchange, buy, copy/paste the address, and withdraw manually. We wanted to embed this flow directly in our app.
The Coinbase Paradox
Here’s what’s frustrating:
Coinbase (the exchange): If a user has a Coinbase account and buys BTC, they CAN withdraw to any Bitcoin address including taproot (bc1p). This is exactly what our users do today — it works.
Coinbase Onramp (the developer widget): Does NOT support Bitcoin L1 as a destination network. Supported networks are only: Base, Ethereum, Optimism, Arbitrum, Polygon, Avalanche, Solana, BNB Chain. You can buy BTC through the widget, but it stays in their Coinbase account — the widget cannot send to a custom Bitcoin address.
Why the gap? Coinbase Onramp seems designed for EVM/smart contract wallets, not Bitcoin L1. The functionality exists on their main platform, just not exposed through their developer API.
Other Options
MoonPay
- Cost: $3,000/year subscription
- Fees: $3.99 minimum / 4.50% per transaction
- Supports: BTC to custom addresses (taproot support needs verification)
- Integration: Embeddable iframe widget
Compare to Coinbase’s fees: 2.5% credit card / 0.5% ACH — MoonPay is significantly more expensive for users, plus the $3k/year is steep for indie builders.
Transak
- Haven’t fully evaluated, unclear if they support taproot addresses
Questions for the Community
- Has anyone found an onramp provider that supports BTC withdrawals to custom taproot (bc1p) addresses with embeddable widget + competitive fees?
- Is there appetite for a shared/subsidized onramp integration that Stacks ecosystem apps could use?
- Should someone reach out to Coinbase about adding Bitcoin L1 support to Onramp? Seems like a natural fit given they already support BTC withdrawals on their main platform.
- For those building with sBTC: what onboarding flow are you using for users who don’t have crypto?
Would love to hear what others have discovered.