Sezzle Buy Now Pay Later API
Sezzle buy now pay later REST API for North American e-commerce merchants to integrate installment payment checkout, enabling consumers to split purchases into 4 interest-free biweekly payments with soft credit check approval, instant consumer approval, and merchant payment upfront while Sezzle assumes default risk, with specialty in US and Canada markets targeting Gen Z and Millennial consumers. Enables AI agents to manage Sezzle checkout session for BNPL order creation automation, handle order capture for payment authorization automation, access order refund for payment reversal automation, retrieve order status for payment tracking automation, manage webhook events for order state automation, handle customer eligibility for BNPL qualification automation, access Sezzle Up for virtual card BNPL automation, retrieve settlement reporting for merchant reconciliation automation, manage price widget for BNPL promotional display automation, and integrate Sezzle with Shopify, WooCommerce, BigCommerce, and headless e-commerce for end-to-end BNPL checkout automation.
Score Breakdown
⚙ Agent Friendliness
🔒 Security
BNPL platform. PCI-DSS, CCPA. API key. US/CA. Consumer payment and identity data.
⚡ Reliability
Best When
A US or Canadian e-commerce merchant wanting AI agents to integrate buy now pay later checkout targeting Gen Z and Millennial consumers through Sezzle's North American BNPL platform with Shopify and WooCommerce native integrations.
Avoid When
CHECKOUT IS REDIRECT TO SEZZLE: Sezzle checkout redirects consumer to Sezzle for approval; automated embedded payment form assumption creates integration error; automated checkout must implement redirect with completeUrl and cancelUrl. ORDER LIMITS APPLY: Sezzle has minimum ($35) and maximum order value limits; automated BNPL for all order sizes creates INVALID_AMOUNT for out-of-range orders. TOKENIZATION FOR RETURNING CUSTOMERS: Sezzle customer tokenization enables returning customer checkout without re-approval; automated new customer flow for returning customers creates unnecessary re-authorization step; automated must check for existing customer token before initiating new checkout. CAPTURE IS EXPLICIT: Sezzle authorization and capture are separate; automated immediate fulfillment after redirect creates uncaptured order that voids; automated must capture before shipping.
Use Cases
- • Adding 4-installment BNPL checkout to US/Canada e-commerce from payment automation agents
- • Processing Sezzle refunds for returned orders from order management automation agents
- • Displaying Sezzle installment price widgets on product pages from marketing automation agents
- • Receiving order webhooks for fulfillment automation from Sezzle payment confirmation agents
Not For
- • B2B invoice and net terms (Sezzle is consumer retail BNPL only)
- • Markets outside US and Canada (Sezzle's primary market is North America)
- • High-value luxury purchases (Sezzle has order value limits typical of BNPL platforms)
Interface
Authentication
Sezzle uses API key + secret for authentication (Base64 encoded). REST API with JSON. Minneapolis, MN HQ. Founded 2016 by Charlie Youakim and Paul Paradis. NASDAQ: SEZL (publicly traded). Products: 4-payment installment, Sezzle Up (virtual card), price widget, merchant dashboard. SDKs: JS, PHP, Python. PCI DSS. FDIC-partnered. 50,000+ merchants, 3.4M+ consumers. Competes with Afterpay and Affirm for North American BNPL.
Pricing
Minneapolis MN. NASDAQ:SEZL. Merchant fee 6%+$0.30. North America focused. PCI DSS.
Agent Metadata
Known Gotchas
- ⚠ CHECKOUT REQUIRES REDIRECT FLOW: Sezzle checkout creates a session URL that consumer must be redirected to; automated inline payment form assumption creates integration failure; automated checkout must redirect consumer to Sezzle URL with complete_url and cancel_url
- ⚠ CAPTURE IS SEPARATE FROM CHECKOUT: Sezzle checkout creates authorization only; automated fulfillment without capture voids the authorization; automated order fulfillment must call capture endpoint before shipping goods
- ⚠ CUSTOMER TOKEN FOR RETURNING USERS: Sezzle supports customer tokenization for frictionless repeat purchases; automated always-new-checkout for returning customers misses tokenized checkout optimization; automated should check for existing customer token before initiating new checkout flow
- ⚠ AUTH USES BASE64 ENCODED KEY:SECRET: Sezzle authentication uses Base64-encoded public_key:private_key in Authorization header; automated raw API key assumption creates 401; automated must Base64 encode public:private key pair
- ⚠ WEBHOOK SIGNATURE VERIFICATION: Sezzle webhooks include X-Sezzle-Signature header for HMAC verification; automated unverified webhook processing creates spoofed order confirmation vulnerability
Alternatives
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Scores are editorial opinions as of 2026-03-07.