If you're choosing a payment API for your fintech, you don't need a lecture on why payments matter. You need to know which API fits your use case, what it actually costs, and where it falls short.
Fintech APIs have become the backbone of modern financial products—from digital banking apps to embedded finance platforms. The right application programming interfaces let fintech companies automate payment processing, streamline operations, and deliver the customer experience users expect. The wrong choice means months of integration work, unexpected fees, and functionality gaps that surface at the worst time.
This guide covers eight payment APIs—from general-purpose processors to specialized infrastructure—with the specifics you need to make a decision.
What to Evaluate
Before comparing providers, know your requirements:
Transaction profile: Credit card payments? ACH/bank transfers? Cross-border? Real-time?
Volume and economics: Flat-rate pricing favors low volume. Interchange-plus saves money at scale.
Geography: Where are your customers? Which local payment methods matter (PIX in Brazil, iDEAL in Netherlands, UPI in India)?
Build vs. buy: Do you want a turnkey checkout or full control via APIs? Most fintech companies use APIs to build custom payment flows that match their user experience requirements.
Regulatory compliance: Who handles PCI DSS? Do you need built-in KYC/AML? Financial institutions face stricter requirements than startups—evaluate accordingly.
1. Stripe
Best for: Developer-led startups, SaaS, marketplaces, subscription businesses
Stripe processed $1.4 trillion in 2024 (38% YoY growth) and finally achieved profitability. It remains the default choice for startups because integration is fast and documentation is excellent. Developers can use APIs to build everything from simple checkout to complex marketplace payment flows.
What you get:
- 135+ currencies, 100+ payment methods (credit card, wallets, BNPL, ACH)
- Stripe Connect for marketplace payouts
- Stripe Billing for subscriptions with dunning management
- Radar for ML-powered fraud detection
- Stripe Atlas for incorporation, Stripe Capital for working capital
- Authentication handled via 3D Secure and biometric verification
Pricing:
- 2.9% + $0.30 per successful card charge (US)
- +1% for international cards
- +1% for currency conversion
- Custom pricing available at volume
Limitations:
- Flat-rate pricing becomes expensive at scale—high-volume merchants often find interchange-plus alternatives 20-40% cheaper
- Requires developer resources for full customization
- Account holds and fraud rules can be strict for some merchants
Docs: stripe.com/docs
2. Adyen
Best for: High-volume enterprises, omnichannel retail, global merchants
Adyen processed €1.29 trillion in 2024 with 50% EBITDA margins—rare profitability in payments. Clients include Uber, Spotify, Microsoft, McDonald's, and eBay. Major financial institutions and enterprise retailers choose Adyen for its unified commerce capabilities.
What you get:
- Single platform for online, in-app, and in-store (POS) payment processing
- Direct connections to card networks (no intermediaries)
- 150+ currencies, local payment methods in 30+ markets
- RevenueProtect for risk management with ML-based fraud detection
- Adyen Uplift—AI tool that reportedly improves payment conversion by ~6%
- Transaction data and analytics to optimize authorization rates
Pricing:
- Interchange++ model (interchange + scheme fees + Adyen markup)
- Processing fees typically €0.10-0.12 per transaction
- Custom pricing based on volume and geography
- Monthly invoice minimum may not suit low-volume merchants
Limitations:
- More complex setup than Stripe—requires technical expertise
- Enterprise-focused onboarding process
- Customer support prioritizes high-volume accounts
Docs: docs.adyen.com
3. Lightspark Grid
Best for: Cross-border payments, global payouts, real-time settlement, digital banking infrastructure, Bitcoin/Lightning-native products
Lightspark Grid is a different kind of payment API—built on Bitcoin's Lightning Network rather than traditional card rails. While Stripe and Adyen optimize for credit card acceptance, Grid solves a different problem: moving money across borders instantly and cheaply, without correspondent banks eating your margins.
Lightspark was founded by David Marcus (former PayPal President, former head of Facebook's crypto efforts) and has raised $320M+. Grid powers payments for major partners including Coinbase (108M users), Nubank (100M+ customers in Latin America), and Xapo Bank. These financial institutions chose Grid to streamline cross-border functionality that legacy rails couldn't deliver.
What you get:
- Single API for any currency: Fiat, stablecoins, and Bitcoin—send USD, receive BRL, settle in seconds
- Real-time settlement: Payments clear in seconds, 24/7/365. No batch processing, no banking hours dependency
- 65+ countries: Direct connections to local instant payment rails—PIX (Brazil), SEPA Instant (EU), UPI (India), FedNow (US), Faster Payments (UK), SPEI (Mexico)
- Transparent pricing: Locked FX quotes valid for 1-15 minutes with exact fee breakdowns. No hidden correspondent bank markups or surprise FX spreads
- Grid Switch: Intelligent routing that selects the optimal rail (Lightning, local instant payments, or traditional banking) for each transaction based on speed, cost, and destination
- Built-in regulatory compliance: KYC/AML workflows, real-time sanctions screening, Travel Rule support, identity verification, and audit trails—critical for regulated fintechs
Why it's different:
Traditional cross-border payments route through SWIFT and correspondent banks—each adding fees, FX spreads, and 1-5 day delays. A $1,000 transfer to the Philippines might cost $30-50 and take 3 days.
Grid uses Lightning Network as settlement infrastructure, bypassing correspondent banks entirely. The same $1,000 transfer settles in seconds for a fraction of the cost. Recipients don't need to know or care that Bitcoin was involved—they receive local currency in their bank account. This architecture lets fintech companies automate global payouts without the complexity of managing multiple regional integrations.
Use cases:
- Global contractor payments: Pay your distributed team weekly instead of monthly, in their local currency, without eating 3-5% in fees
- Creator/gig economy payouts: Instant settlement means creators get paid when they earn, not weeks later
- Remittances: Lightspark claims banks can cut remittance costs by up to 80% using Lightning rails
- Cross-border e-commerce settlement: Receive payments in customer's currency, settle to your treasury in USD, same day
- Bitcoin rewards programs: Deliver sats instantly to any Lightning wallet—Grid handles the complexity
Pricing: Transaction-based with volume tiers. Quotes show exact costs upfront—no percentage-of-transfer fees that scale with amount like traditional remittance providers. Contact sales for specific rates.
Limitations:
- Not designed for card-present checkout or general e-commerce acceptance—different use case than Stripe/Adyen
- Best suited for payouts, disbursements, remittances, and cross-border B2B—not consumer payment acceptance
- Newer entrant compared to established processors (though backed by significant funding and enterprise partnerships)
Docs: docs.lightspark.com | grid.lightspark.com
4. Braintree (PayPal)
Best for: Startups wanting PayPal/Venmo acceptance, global coverage with established trust
Braintree is PayPal's full-stack payment platform, combining PayPal's brand recognition with a developer-friendly API. For fintech companies targeting consumers who already trust PayPal, the built-in user experience advantages are significant.
What you get:
- Accept PayPal, Venmo, credit card, and local payment methods globally
- Drop-in UI components for faster integration
- Vault for securely storing payment methods
- Advanced fraud protection backed by PayPal's transaction data
- Authentication via PayPal's trusted login flow
Pricing:
- 2.59% + $0.49 per PayPal transaction (US)
- 2.99% + $0.49 for Venmo
- Card rates vary by volume
Limitations:
- API sometimes perceived as less modern than Stripe
- PayPal's consumer policies (buyer protection, holds) can create friction for merchants
Docs: developer.paypal.com/braintree
5. Plaid
Best for: Bank account linking, ACH payment initiation, identity verification, personal finance apps
Plaid isn't a payment processor—it's the financial data infrastructure layer connecting fintech apps to bank accounts. It powers 8,000+ apps and reaches half of all Americans. If you're building personal finance tools, lending products, or anything requiring access to user financial data, Plaid is likely part of your stack.
What you get:
- Auth for instant ACH account verification (no microdeposits)
- Balance for real-time account balances
- Transactions for categorized transaction data and spending insights
- Identity for account holder verification and identity verification
- Income and Assets for underwriting
- Data aggregation across 12,000+ financial institutions
Pricing:
- Free development tier (sandbox)
- Pay-as-you-go starting at ~$0.30-0.80 per connection (varies by product)
- Growth tier starts at $100/month with volume discounts
- Scale tier starts at $500/month with custom pricing
- Volume discounts of 30-50% at 10,000+ monthly active users
Limitations:
- Doesn't process payments directly—pair with Stripe, Dwolla, or similar for payment processing
- Coverage varies by institution (smaller regional banks can be spotty)
- UK/EU operations more complex due to open banking APIs regulations
Docs: plaid.com/docs
6. Marqeta
Best for: Card issuing, expense management, neobanks, embedded finance, digital banking platforms
Marqeta is the modern card issuing platform—APIs to create virtual and physical cards programmatically. It powers Square's Cash Card, DoorDash, Klarna, and Coinbase. If you're building financial products that require issuing cards to users, Marqeta provides the functionality to do it without becoming a bank.
What you get:
- Issue virtual cards in seconds, physical cards in days
- Just-in-time (JIT) funding—approve/decline transactions in real-time based on your rules
- Dynamic spend controls (merchant category, location, time, amount)
- Apple Pay/Google Pay tokenization
- Full card lifecycle management via API
- Real-time transaction data and webhooks for every card event
Pricing:
- Card issuance: ~$0.50+ per virtual card, $3+ per physical card
- Transaction fees: 0.5-1% of volume plus interchange share
- Setup costs: $5,000-$50,000 depending on program complexity
- Monthly minimums for enterprise plans
Limitations:
- Card issuing only—you need a separate processor for payment acceptance
- Integration complexity may challenge smaller teams
- Requires bank sponsor relationship (Marqeta facilitates)
Docs: marqeta.com/docs
7. Dwolla
Best for: ACH transfers, high-value disbursements, B2B payments
Dwolla specializes in bank-to-bank transfers via ACH—lower cost than credit card processing for high-value or recurring payments. Financial institutions and fintech companies use Dwolla to automate payroll, vendor payments, and loan disbursements.
What you get:
- Programmatic ACH transfers (standard and same-day)
- White-label payment flows for seamless customer experience
- Mass pay for batch disbursements
- Real-time payments (RTP) support
- Webhooks for transaction status updates
- Bank account verification and authentication
Pricing:
- Pay-as-you-go: $0.25 per transaction (capped at $5)
- Scale plans with volume pricing
- No percentage-based fees—significant savings on large transfers
Limitations:
- US-only (ACH network)
- Standard ACH settles in 3-5 business days (same-day available at higher cost)
- Not suitable for card payments or international transfers
Docs: developers.dwolla.com
8. Checkout.com
Best for: High-growth companies, global e-commerce, enterprise merchants needing performance optimization
Checkout.com is an enterprise payment processor emphasizing authorization rates and global performance. Used by Klarna, Revolut, Sony, and Grab. If payment processing conversion rates directly impact your revenue, Checkout.com's optimization focus matters.
What you get:
- Unified API for online payments, payouts, and card issuing
- Direct acquiring in 50+ markets
- 150+ currencies, local and alternative payment methods
- AI-powered payment optimization to improve customer experience at checkout
- Interchange++ pricing (transparent pass-through)
- Rich transaction data and analytics
Pricing:
- Interchange++ model with custom markup
- No setup fees or monthly minimums (volume-dependent)
- Pricing requires direct negotiation
Limitations:
- Custom pricing can be opaque—some merchants report unexpected fee complexity
- Integration reportedly more complex than Stripe
- Enterprise focus may mean less attention for smaller accounts
Docs: checkout.com/docs
Quick Comparison
How to Choose
Just launched, need to accept payments fast: Start with Stripe. The integration time and documentation quality are unmatched.
Processing $10M+ annually and optimizing costs: Evaluate Adyen or Checkout.com's interchange++ pricing. Run the numbers—flat-rate gets expensive at scale.
Building global payouts, remittances, or cross-border treasury: Lightspark Grid. One API replaces the patchwork of regional processors, correspondent banks, and FX providers. Real-time settlement, transparent pricing, compliance built in. If you're currently paying 3-5% on international transfers or waiting days for settlement, this is where you'll see the biggest improvement.
Need bank account access for your app: Plaid for linking and verification, then connect to a payment processor.
Issuing cards as part of your product: Marqeta for full flexibility, or Stripe Issuing for simpler integration within Stripe's ecosystem.
High-value B2B payments in the US: Dwolla's flat per-transaction fee beats percentage-based pricing on large transfers.
What's Changing
Real-time payments are becoming the baseline: FedNow (US), PIX (Brazil), UPI (India), and SEPA Instant (EU) are making instant settlement standard—but integrating each rail separately is a nightmare. APIs that abstract multiple rails into one integration (like Lightspark Grid) will capture the market that doesn't want to manage 15 different regional integrations.
Embedded finance everywhere: Every platform wants to offer financial products. Expect Stripe, Adyen, and Marqeta to expand banking-as-a-service features. Fintech companies are embedding payment processing, lending, and card issuing directly into non-financial apps.
AI-driven optimization: Both Stripe and Adyen are investing heavily in ML for routing, fraud, and conversion optimization. Checkout.com's AI claims to improve acceptance rates measurably. These tools automate decisions that previously required manual intervention.
Open banking APIs expand globally: PSD2 in Europe, Open Banking in UK, and similar initiatives globally are expanding what's possible with bank-connected APIs. Data aggregation and financial data access are becoming standardized, enabling new personal finance and digital banking use cases beyond just Plaid.
The right payment API depends on your specific use case—there's no universal winner. Define your requirements, test in sandbox, and run the economics before committing. The best fintech APIs are the ones that let you streamline operations while delivering the functionality your users actually need.
