ADR — WAHA over Meta Cloud API for WhatsApp

TL;DR

Use WAHA (unofficial WhatsApp HTTP API) self-hosted on a VPS for outbound notifications and admin messaging. Meta Cloud API is too expensive at MVP volume.

Context

• Required: 1-hour-before class WhatsApp reminder, admin manual messages, OTP-style notifications.
• Volume: small (few hundred messages / month at MVP).
• Meta Cloud API: requires Business verification, template approval, per-message fees that don't suit current volume / cash flow.

Decision

Run WAHA in Docker on a personal VPS. Use one WhatsApp number for outbound. Rotate or upgrade to Meta Cloud API only if the number is banned or volume crosses a threshold making fees comparable.

Consequences

• WhatsApp number ban risk is real and increases with frequency / templated-marketing-style messages.
• WAHA sessions drop silently — operational toil; keep a restart checklist in the application operations docs.
• No template approval = ToS gray zone.
• Cheap and flexible.

Alternatives Considered

• Meta Cloud API: rejected due to cost / overhead at MVP.
• Email-only fallback: insufficient for the WhatsApp-first audience.
• Twilio: priced in USD, expensive.

Related ADRs

• ADR — billing handover

References

• Operational checklist (external app docs): ops/waha-session-restart.md
• Future-state backlog item to revisit if banned: TBD when triggered.