RocketDrop

The problem

Selling the same electronics inventory across eight marketplaces and a direct storefront meant checkout, stock counts and payment reconciliation were being handled separately per channel, so a sale on one channel could oversell stock on another.

Business challenge

Process orders and keep inventory in sync across eight-plus marketplaces and carriers, without overselling stock or violating any marketplace order rules.

Research

Reviewed the order and inventory contract of every connected marketplace and carrier API - Amazon, Walmart, eBay, Newegg, Rakuten, BestBuy, FedEx, UPS, USPS and DHL - to find where one internal order model could satisfy all of them.

Planning

Centralised checkout, order processing and inventory sync behind one internal order API, with every marketplace and carrier integration built as an adapter against it instead of a one-off script per channel.

Architecture

• Order-processing API in front of checkout, marketplace orders and admin flows
• Marketplace adapters for Amazon, Walmart, eBay, Newegg, Groupon, Rakuten, BestBuy and Facebook
• Shipstation-based fulfilment with FedEx, UPS, USPS and DHL integration
• QuickBooks Desktop SDK sync for accounting and payment reconciliation

Database design

Order and inventory data centralised so stock reserved through one channel is reflected everywhere else, with the QuickBooks sync running as a downstream integration rather than the source of truth.

API flow

1. 1 Order comes in from the storefront or a connected marketplace
2. 2 Order API validates and reserves inventory before confirming
3. 3 Shipstation and the carrier integrations handle fulfilment
4. 4 QuickBooks Desktop SDK syncs the completed order for accounting

Implementation

• Built marketplace integrations as adapters against one internal order model instead of per-channel one-offs
• Wired Shipstation and four carrier APIs into a single fulfilment step
• Integrated the QuickBooks Desktop SDK so completed orders sync to accounting automatically
• Added Twilio and Google Sheets integrations for order notifications and reporting

Key features

• Unified checkout across the storefront and connected marketplaces
• Real-time inventory sync across eight-plus sales channels
• Automated fulfilment via Shipstation and four major carriers
• QuickBooks Desktop SDK accounting sync

Performance

• One order model absorbed eight-plus marketplace integrations without per-channel special-casing
• Fulfilment and accounting sync run as automated steps instead of manual exports

Lessons learned

• Build one internal order model first - every marketplace API becomes an adapter instead of a special case.
• Accounting sync is happiest as a downstream consumer of order state, not a dependency of checkout.