Yosync

The problem

Merchants who run their business from Notion copy orders and products over by hand or with CSV exports, which are out of date the moment they're made.

What I did

• Built both login flows, for Shopify and for Notion, and a sync engine that combines real time webhooks with a scheduler that runs every 15 minutes.
• Found and closed a real security hole: the Notion connection step didn't check who was asking, so anyone who knew a store's address could take over its Notion connection. Fixed with session checks and a signed login state.
• Fixed silent data loss: syncs only fetched the first 100 records, so busy stores could lose changes. Added proper paging, and a retry so a capped run tries again instead of skipping records.
• Stopped one failing request from crashing the server for every store by handling errors in every route.
• Added billing through Shopify ($19 a month after a 14 day trial) and wrote the App Store listing.

The result

I'm now reworking Yosync as a custom app, installed directly for individual stores.