WhatsApp Business API integration for a construction-management SaaS (Node (express.js) + React)

We build a SaaS used by construction companies in Argentina to manage projects, budgets, purchases, subcontractors and invoicing. The app already generates PDF documents and can email them. We want users to send those same documents to their clients, suppliers and subcontractors over WhatsApp with one click, and later to receive documents through WhatsApp too. Phase 1: outgoing documents (main scope) Integrate the WhatsApp Business Platform: Meta Cloud API directly, or a provider such as Twilio or 360dialog. We’d like your recommendation, with costs. Add a “Send by WhatsApp” action next to the existing “Send by email” action for: Budgets (presupuestos) → client Client invoices → client Purchase orders → supplier Subcontract agreements and subcontract payment receipts → subcontractor Upload the generated PDF as a WhatsApp document message, using a Meta-approved template (Spanish), with the recipient’s phone pre-filled from their record and editable before sending. Normalize phone numbers to E.164, including the Argentine mobile format (+54 9 …). Record each send (who, what, when, delivery/read status from webhooks) and show it on the document. Show failures in plain language (number not on WhatsApp, template rejected, etc.). Tech stack Backend: Node (Express), PostgreSQL, QuestPDF, multi-tenant (each company is a separate tenant) Frontend: React + TypeScript (Vite), React Query You’ll work inside our existing services and UI patterns. This is not a separate microservice. Must have Proven production experience with the WhatsApp Business API: templates, media/document messages, webhooks, the 24-hour session window Strong Node (Express.js) comfortable with React + TypeScript Experience with Meta Business verification and number onboarding Spanish is a big plus (templates and UI are in Spanish) Deliverables Working Phase 1 merged into our repos, with tests for the sending and webhook logic Setup guide: Meta/provider account, templates, environment variables, webhook URL A short cost estimate per message for our volume In your proposal, please answer: Should each customer company connect its own WhatsApp number (Embedded Signup), or should everyone send from one shared number of ours? What are the pros and cons? Meta Cloud API directly, or a provider? Why? A WhatsApp integration you’ve shipped, and roughly how long Phase 1 would take you.