API Development for UK eCommerce -- Compliance Built In

UK eCommerce API Architecture 2026

UK eCommerce APIs in 2026 are shaped by four integration patterns: (1) Shopify Storefront API (GraphQL -- headless commerce front-end, cart management, product catalogue -- SAQ-A PCI scope), (2) payment APIs (Stripe Elements SAQ-A, GoCardless BACS Direct Debit, Klarna BNPL -- Consumer Credit Act 1974 for BNPL), (3) ERP/OMS integrations (Brightpearl, NetSuite, Linnworks -- inventory, order management, fulfilment), (4) carrier APIs (Royal Mail Click and Drop, DPD, Evri -- shipping label generation, tracking). UK-specific: UK Consumer Rights Act 14-day return right, HMRC VAT API (MTD -- digital VAT for e-commerce businesses above GBP90,000 VAT threshold), Authorised Push Payment (APP) fraud reimbursement obligations from PSR regulations.

Shopify Storefront API Integration

Shopify Storefront API (GraphQL): the API layer for headless Shopify commerce. Key operations: (1) product queries (product by handle, products by collection, product by ID -- all cacheable via ISR), (2) cart management (cart create, cart lines add/remove/update -- stored in Shopify, not local state), (3) checkout initiation (cart to checkout redirect -- Shopify handles checkout, PCI-DSS SAQ-A), (4) customer account (customer access token -- order history, address management), (5) search (predictive search, full product search -- Shopify Storefront Search API). Performance: Shopify CDN for product images (WebP, < 100KB, lazy-loaded below fold). UK tax: Shopify handles UK VAT (20% standard, 0% for children clothing, food -- Shopify UK tax engine). Shopify Markets: UK + EU pricing (DDP -- Duties and Taxes Paid) for EU post-Brexit.

Klarna BNPL UK Consumer Credit Act

Klarna BNPL (Buy Now Pay Later) UK integration: Klarna is FCA-regulated from 2026 (previously unregulated -- FCA Consumer Credit authorisation required). Klarna UK integration: (1) Klarna checkout widget (Klarna.js -- iframe embed, SAQ-A PCI scope similar to Stripe Elements), (2) consumer credit disclosure (FCA Consumer Credit Act 1974 -- Klarna must display APR, total cost of credit, cancellation rights before BNPL agreement), (3) affordability check (Klarna performs affordability check -- retailer must not present BNPL in a way that bypasses Klarna affordability check), (4) FCA Consumer Duty (BNPL presented fairly -- not as default option, not as primary payment method before customer has seen the price), (5) Customer complaint handling (FCA DISP -- BNPL complaints handled within 8 weeks). Post-FCA regulation: ClickMasters Klarna integration template updated for FCA regulated BNPL disclosure requirements.

Royal Mail Click and Drop API

Royal Mail Click and Drop API: UK domestic shipping automation. Integration: (1) order import (order data from OMS to Click and Drop -- weight, dimensions, value, recipient address), (2) service selection (Royal Mail service -- Tracked 24, Tracked 48, Special Delivery, International Tracked -- based on order value and destination), (3) label generation (Royal Mail barcode label -- printed at packing station), (4) manifest creation (end of day manifest -- submits all orders to Royal Mail for collection), (5) tracking webhook (Royal Mail tracking updates via webhook -- order status updated in OMS, customer notification via email). UK address validation: Royal Mail PAF (Postcode Address File) validation -- prevents labels failing Royal Mail quality check. Returns: Royal Mail Tracked Returns label generated at order level -- downloadable by customer.

UK Consumer Rights Act

PECR

UK GDPR

PCI-DSS SAQ-A

WCAG 2.1 AA

Cyber Essentials