Full-stack developer for a real-time multiplayer web app (mobile-first, Shopify integration)

I’m building a mobile-first web app where small groups (2–5 players) play a timed, stage-based game together, each on their own phone. Details of the concept will be shared with shortlisted candidates after signing an NDA. Technical scope: Lobby with invitations by link or QR code Real-time sync across all players’ phones, with reconnection support Different content for each player at each stage, with answers checked on the server only Hints, timer, pause and resume, scoring and a shareable results screen A scripted (non-AI) in-game chat with text managed from an admin panel Admin panel with two-factor login: content management, game overview, reports and CSV export Shopify integration: a paid order automatically creates a unique game, and its link is added to the order confirmation email Custom UI design included Requirements: I can add new content myself without a developer English only Staging site for testing each milestone All accounts and code owned by me from day one Documentation and 30 days of bug fixes after launch Payment: fixed price by milestone, starting with a small paid discovery phase. Please start your proposal with the word BRIEFCASE so I know you’ve read this.