Voice

Deliver a pre-recorded audio message to PSTN numbers — up to 1,000 destinations in a single request.

curl -X POST https://api.9bits.net/voice/v1/voice/sendvoice \
  -H "Authorization: Bearer $NINEBITS_TOKEN" \
  -H "Content-Type: application/json" \
  -d '{
    "to": ["2348020000000", "2348030000000"],
    "media_url": "https://cdn.example.com/audio/reminder.mp3"
  }'

You host the audio; we fetch it, transcode it for GSM voice, and play it when the call is answered.

Two things to know up front

The webhook is not optional

Voice has no polling endpoint. There is no GET /calls/{id}.

The webhook is the only way to learn whether a call connected, how long it lasted, or what it cost. If you don’t configure one under Settings → Webhook, you will have no idea what happened to your calls.

Set it up before your first send.

Your media URL must stay up

We fetch media_url at dispatch time, not when you call the API. If the URL is unreachable then — expired signed URL, a redeploy, an origin behind auth — the call fails.

Host the file somewhere stable and public, and keep it there for the life of the campaign.

Caller ID

Your account is provisioned with a caller ID automatically at signup. You can omit from and we’ll use it.

If your account has several, one is chosen at random. When it matters which number appears — and for anything customer-facing it usually does — pass from explicitly.

Billing

You’re billed on call_duration, not total_duration:

Field	What it measures
total_duration	Wall-clock, including ring time
call_duration	Billed — connected time only

Both arrive on the webhook, along with total_amount.

Start here

Send a voice message The request, the response, and the call-result webhook.

Try it live Run it against your account from the browser.

Webhooks Required for voice — set it up before you send.