# Delivery states and safe fallback

Use terminal failure, consent, deduplication, and a one-fallback limit to recover delivery without sending duplicate or prohibited messages.

## Recommended state machine

```text
queued -> accepted/sent -> delivered -> read
                    \-> failed -> classify -> optional one-time fallback
```

`accepted` or `sent` is not failure. Do not resend merely because `delivered` has not arrived within a short polling interval. Provider receipts can be delayed.

## Classify the terminal failure

| Failure class | Fallback? | Action |
|---|---|---|
| Temporary transport or disconnected session | Sometimes | Apply a cooling period, then use one approved alternate channel if consent permits |
| Invalid recipient or address | No | Correct the contact record before another attempt |
| Opt-out, block, complaint, or consent failure | No | Suppress the recipient across the campaign or purpose |
| Template, category, quality, account, or policy rejection | No automatic fallback | Fix the policy or account condition; do not route around it |
| Duplicate or already delivered business event | No | Mark complete and suppress every later attempt |

## Fallback invariants

1. One stable business-event ID controls every channel attempt.
2. One recipient, purpose, message, and doctor or clinic sender stay attached to that event.
3. Only a terminal `failed` state can enter fallback evaluation.
4. Allow at most one fallback attempt unless a human explicitly approves another.
5. Re-check consent, suppression, and recipient identity immediately before fallback.
6. Never fall back after an opt-out, block, complaint, or policy/quality failure.
7. If a late `delivered` or `read` event arrives after fallback began, suppress any unsent duplicate and record both states.

## A practical hybrid for healthcare notifications

- Send approved appointment, recall, or operational templates through the WhatsApp Business Platform as the primary path.
- If that specific attempt reaches a recoverable terminal transport failure, offer one consented recovery path: a low-volume message from the same clinic's linked WhatsApp number, an SMS, an email, or a Customer Room notification.
- Keep clinical detail out of the fallback message unless the channel, purpose, legal basis, and security controls permit it. A neutral prompt to open the private Customer Room often carries less sensitive content.

## Measure the journey

Track acceptance rate, terminal-failure rate, delivered rate, duplicate-prevention count, fallback rate, fallback delivery, opt-outs, complaints, and time to delivery. Separate transport recovery from recipient engagement; a read receipt is not a medical outcome.

For WhatsApp Web constraints, read [Safe use of a WhatsApp Web connection](/whatsapp-web/safe-use).

Canonical: https://docs.bow.chat/developers/delivery-and-fallback
Version: 1
Updated: 2026-09-04T10:04:30.711Z