Nixflex - AI Voice Platform for Building AI Phone Agents

SMS campaigns send the same message (or templated variations) to many recipients in one API call. Useful for promotions, appointment batches, announcements, and reminders.

Campaigns are one-time broadcasts. They send the message and stop. When a recipient replies, the reply is handled by the SMS agent on that number - not by the campaign itself.

How replies work

A campaign only sends. When a recipient texts back, the reply is answered by the SMS agent on that number, using that number’s own SMS instructions (its sms_prompt) - the same agent that answers every inbound text. The campaign message is not carried into the reply automatically. If you want the agent to handle replies about a promotion, put the promotion details in the number’s sms_prompt before you launch. Otherwise the agent does not know the campaign went out. For example, add to the number’s sms_prompt:

We are running a March promotion: 20 percent off cleanings, valid weekdays 9am-5pm next week. If a customer replies YES, confirm the offer and ask which day suits them. Then when someone replies YES - or asks about the offer - the SMS agent already knows what to say, and can even book them in if the number has a booking calendar connected. See the SMS agent page for the full reply behaviour.

Campaigns run from Twilio and Telnyx numbers alike. The From number decides which of your carrier accounts sends the messages and which one bills you for them.

Create a campaign (API)

curl -X POST https://api.nixflex.com/v1/sms/campaigns \
  -H "Authorization: Bearer KEY_ID:KEY_SECRET" \
  -H "Content-Type: application/json" \
  -d '{
    "agent_id": "agent_125207e452f8714a",
    "from_number": "+447446466847",
    "name": "March promotion",
    "message_template": "Hi {{first_name}}, Acme Dental offering 20% off cleanings this month. Reply YES to book.",
    "recipients": [
      { "phone": "+447111000001", "variables": { "first_name": "Sarah" } },
      { "phone": "+447111000002", "variables": { "first_name": "James" } }
    ],
    "schedule_type": "now"
  }'

Response:

{
  "campaign_id": "smsc_a1b2c3d4",
  "status": "running",
  "total_count": 2,
  "delivered_count": 0,
  "failed_count": 0,
  "pending_count": 2,
  "source": "api"
}

Personalization with placeholders

Use {{variable_name}} in your message_template. Each recipient’s variables object fills the placeholders. Template: Recipient:

{
  "phone": "+447111000001",
  "variables": {
    "first_name": "Sarah",
    "day": "Tuesday",
    "time": "2pm"
  }
}

Sent SMS: Hi Sarah, your appointment is on Tuesday at 2pm. If a placeholder has no matching variable, it renders as an empty string (no crash). Same pattern as Twilio, SendGrid, and Mailchimp.

From the dashboard

In the dashboard, Outbound → SMS Campaigns → New Campaign, you can add recipients two ways:

Paste numbers: drop in a list separated by commas, tabs, spaces, or newlines. The form auto-detects phones (E.164 format) and any extra columns become variables.
Upload CSV: drag-and-drop or browse. The form auto-detects the phone column from headers (phone, number, mobile, tel, telephone) and treats all other columns as variables.

Either way you get a preview table before sending.

Scheduling

Send later instead of now:

{
  "schedule_type": "schedule",
  "scheduled_at": "2026-05-20T09:00:00Z"
}

Campaign sits at status: scheduled until the time arrives. You can cancel it before then with DELETE /v1/sms/campaigns/:id.

Tracking delivery

Get campaign status:

curl https://api.nixflex.com/v1/sms/campaigns/smsc_a1b2c3d4 \
  -H "Authorization: Bearer KEY_ID:KEY_SECRET"

Response:

{
  "campaign_id": "smsc_a1b2c3d4",
  "name": "March promotion",
  "status": "done",
  "total_count": 100,
  "delivered_count": 95,
  "failed_count": 3,
  "pending_count": 2,
  "source": "dashboard",
  "recipients": [
    {
      "phone": "+447111000001",
      "variables": { "first_name": "Sarah" },
      "status": "delivered",
      "twilio_sid": "SM1234567890"
    }
  ]
}

How counts are calculated

Counts come from per-recipient status, not from a cached field. Same logic in the dashboard and the API — they always match.

Count	Calculation
`delivered_count`	Recipients with status `delivered`
`failed_count`	Recipients with status `failed`, `undelivered`, or `sent`
`pending_count`	Recipients with status `pending` or `queued`
`total_count`	All recipients

Why does sent count as failed? Twilio’s sent status only means Twilio handed the message off to the carrier — not that it reached the handset. Carrier confirmation comes as delivered. We treat anything that did not reach delivered as failed, so what you see in the dashboard matches what really happened.

Campaign status

Status	Meaning
`draft`	Created but not launched
`scheduled`	Will launch at `scheduled_at`
`running`	Currently sending
`done`	All recipients processed
`failed`	All recipients failed at submission

Per-recipient status

Status	Meaning	Shown in UI as
`pending`	Just queued by Nixflex	Pending
`queued`	Sent to Twilio API	Pending
`sent`	Twilio handed to carrier (no delivery confirmation)	Failed
`delivered`	Carrier confirmed delivery to handset	Delivered
`undelivered`	Carrier rejected	Failed
`failed`	Twilio itself failed	Failed

List campaigns

curl https://api.nixflex.com/v1/sms/campaigns \
  -H "Authorization: Bearer KEY_ID:KEY_SECRET"

Returns all campaigns for your account, newest first. Each one includes computed counts.

Cancel a campaign

curl -X DELETE https://api.nixflex.com/v1/sms/campaigns/smsc_a1b2c3d4 \
  -H "Authorization: Bearer KEY_ID:KEY_SECRET"

Cancels a scheduled or running campaign. Already-sent messages are not recalled. A done campaign cannot be cancelled.

Source tracking

Every campaign records where it came from in the source field: "dashboard" or "api". The dashboard shows this as a badge so you can tell at a glance which campaigns came from automation versus manual sends.

Rate limiting

Twilio rate-limits SMS at ~1 message per second per number by default. The engine paces sends to respect this. A 1,000-recipient campaign takes roughly 20 minutes to send fully. Need faster? Request a higher MPS limit from Twilio support, or add more sending numbers.

Compliance

Bulk SMS has stricter rules than one-off messages.

UK: All recipients must have opted in. Honour STOP keywords. Keep records of consent.
US: Requires A2P 10DLC registration. Unregistered traffic is blocked by carriers.

Sending without consent risks carrier blocking, fines, and your sending number being flagged as spam.

Costs

Same per-message Twilio billing as one-off SMS. No platform markup. Budget accordingly for large campaigns.

Get started

Guides

Best practices

Core concepts

In-call actions

Features

SMS

Reference

SMS campaigns

How replies work

Create a campaign (API)

Personalization with placeholders

From the dashboard

Scheduling

Tracking delivery

How counts are calculated

Campaign status

Per-recipient status

List campaigns

Cancel a campaign

Source tracking

Rate limiting

Compliance

Costs

​How replies work

​Create a campaign (API)

​Personalization with placeholders

​From the dashboard

​Scheduling

​Tracking delivery

​How counts are calculated

​Campaign status

​Per-recipient status

​List campaigns

​Cancel a campaign

​Source tracking

​Rate limiting

​Compliance

​Costs

How replies work

Create a campaign (API)

Personalization with placeholders

From the dashboard

Scheduling

Tracking delivery

How counts are calculated

Campaign status

Per-recipient status

List campaigns

Cancel a campaign

Source tracking

Rate limiting

Compliance

Costs