Multisite WordPress Car Booking Plugin

I need a single booking engine that lets visitors on several different WordPress sites reserve cars by choosing a “from” date & time and a “to” date & time. All sites must draw their data from one central backend so that availability is always in sync—if a car is booked on Site A it instantly disappears from the calendars on Sites B and C.

Core functions I expect
• Real-time availability tracking across every site
• Automatic booking-confirmation emails to the customer and to an admin address I specify
• Secure online payments processed through Mollie (other gateways can remain optional as long as Mollie works flawlessly)

Tech outline
• WordPress plugin or embeddable module that I can drop into each site via shortcode or Gutenberg block
• Central dashboard (multisite network, external SaaS panel, or custom admin—open to the approach) where I create car entries, set pricing, block dates, and view bookings
• Clean REST or GraphQL endpoints so future mobile apps can hook in
• Front-end calendar/selector that is responsive and lightweight—vanilla JS or React is fine, just keep page speed high
• GDPR-compliant data handling

Deliverable is the working plugin/module, installation guide, and brief hand-over call or video detailing how to add new sites to the system and create additional car objects.