AI-Powered Event Management with Smart Quotation and Automated GST Invoicing

Event management workflows often depend on manual quotation preparation, inventory checking, booking coordination, payment tracking, and invoice generation. This paper presents an AI-powered event management system that combines smart quotation generation with deterministic business rules for booking, payment, GST calculation, and invoicing. The system uses a Next.js frontend, NestJS backend, PostgreSQL hosted on Supabase, Prisma ORM, Google Gemini 2.5 Flash, and Razorpay Sandbox. Customers provide event type, area, and selected requirements; the backend retrieves authoritative catalog data and sends structured context to the AI module. Gemini returns a validated quotation containing suggested items, pricing, GST information, a budget alternative, and a plain- language explanation. A rule-based fallback engine is used when the AI service encounters an API error, timeout, rate limit, or schema- validation failure. Financial calculations remain server-side and use decimal arithmetic. Implementation verification includes 73 passing backend unit tests across 10 suites, 10 AI quotation scenarios, four fallback conditions, ten concurrent invoice-number requests with zero duplicates, a successful frontend production build across nine routes, and an end-to-end booking, sandbox-payment, GST-invoice, and PDF-download workflow. The results demonstrate the feasibility of combining generative AI with deterministic validation and transaction logic for a practical event-management application.