# Multi-tenant WhatsApp API: one key for all your customers

A multi-tenant WhatsApp API lets a software publisher give each of its customers their own WhatsApp number, isolated from the others. With Nodium, each customer is a client of your account: one API key drives them all, and one header names the customer a call acts for.

## The model

- **A client** per customer (`POST /tenants`), with your own `externalId`: use your identifier everywhere a client id is expected.
- **Isolation**: each client has its own numbers, conversations, contacts and templates. A resource of another client answers `404`.
- **One key**: add `Nodium-Tenant: <id or externalId>` to any call. Or issue a key pinned to one client, which can never act on another.
- **One webhook**: a subscription on your own company receives the events of every client, each payload carrying the client it comes from.

```bash
# Same key, one header: the call acts for that customer
curl https://nodium.io/api/v1/messages \
  -H "Authorization: Bearer $NODIUM_KEY" \
  -H "Nodium-Tenant: cust_1042" \
  -H "Content-Type: application/json" \
  -d '{ "channelId": "<channel id>", "to": "+33612345678", "type": "text",
        "text": "Your glasses are ready.", "idempotencyKey": "order-1042-ready" }'
```

## Connecting each customer's number

Each customer connects their own number from a [hosted connect link](https://nodium.io/en/features/embedded-signup), without creating a Nodium account. The number stays theirs, and Meta bills its fees to their own WhatsApp Business account.

## What it costs

A client is free. Your plan is priced on the numbers connected and the messages carried, pooled across all your clients. See [pricing](https://nodium.io/en/pricing).

## Frequently asked questions

### Can one of my customers see another customer's messages?

No. Every resource belongs to one client, and a call acting for one client cannot read another: it answers 404, as if the resource did not exist.

### Do I need one webhook per customer?

No. One subscription on your own company receives the events of all your clients. A subscription created for one client receives that client's events only.

Updated 2026-11-10 · https://nodium.io/en/features/multi-tenant