Welcome to the Text.lk API documentation – Send Flash SMS guide. This section explains how to send Flash SMS (Class 0 messages) using the Text.lk platform.

Flash SMS messages appear directly on the recipient’s screen instead of being stored in the inbox, making them ideal for urgent alerts, OTPs, and high-priority notifications.

What is a Flash SMS? #

A Flash SMS (or Class 0 SMS) is a text message that appears immediately on a recipient’s screen, bypassing the inbox, and usually disappears once dismissed, often without being saved. It grabs instant attention, making it ideal for emergencies, urgent alerts, and one-time passwords (OTPs).

👉 See also: What is a Flash SMS

A Flash SMS is a special type of message that:

• Instantly pops up on the recipient’s device
• Is not saved in the inbox (in most devices)
• Has higher visibility than normal SMS
• Is commonly used for:
  • OTP verification
  • Security alerts
  • Urgent notifications

How to Send Flash SMS #

To send a Flash SMS using Text.lk API, you simply need to include the following parameter in your request:

"is_flash": true

"is_flash": true

Authentication Methods #

Text.lk supports two methods for sending Flash SMS:

OAuth 2.0 (Bearer Token) – Recommended #

This is the secure and production-ready method.

Endpoint #

https://app.text.lk/api/v3/sms/send

https://app.text.lk/api/v3/sms/send

Example Request (Flash SMS) #

curl -X POST https://app.text.lk/api/v3/sms/send \
-H "Authorization: Bearer YOUR_API_TOKEN" \
-H "Content-Type: application/json" \
-H "Accept: application/json" \
-d '{
  "recipient": "94710000000",
  "sender_id": "TextLKDemo",
  "type": "plain",
  "message": "Your OTP is 123456",
  "is_flash": true
}'

curl -X POST https://app.text.lk/api/v3/sms/send \
-H "Authorization: Bearer YOUR_API_TOKEN" \
-H "Content-Type: application/json" \
-H "Accept: application/json" \
-d '{
  "recipient": "94710000000",
  "sender_id": "TextLKDemo",
  "type": "plain",
  "message": "Your OTP is 123456",
  "is_flash": true
}'

Key Notes #

• Uses the POST method
• Data sent as JSON
• Secure (token not exposed in URL)
• Recommended for:
  • Web apps
  • Mobile apps
  • Backend systems
  • Production environments

HTTP GET Method (API Token in URL) #

This is a simple and quick integration method.

👉 See also: How to get Text.lk API Key / API Token

Endpoint #

https://app.text.lk/api/http/sms/send

https://app.text.lk/api/http/sms/send

Example Request (Flash SMS) #

https://app.text.lk/api/http/sms/send?recipient=94710000000&sender_id=TextLKDemo&type=plain&message=Your%20OTP%20is%20123456&is_flash=true&api_token=YOUR_API_TOKEN

https://app.text.lk/api/http/sms/send?recipient=94710000000&sender_id=TextLKDemo&type=plain&message=Your%20OTP%20is%20123456&is_flash=true&api_token=YOUR_API_TOKEN

Key Notes #

• Uses the GET method
• Parameters passed via URL
• Easy to test in a browser
• Recommended for:
  • Legacy systems
  • Quick testing
  • Systems without header support

When to Use Flash SMS #

Use Flash SMS when:

• You need instant user attention
• Sending One-Time Passwords (OTP)
• Delivering critical alerts or warnings
• Ensuring the message is seen immediately

Important Notes #

• Not all devices handle Flash SMS identically (some may still store the message)
• Overusing Flash SMS can reduce effectiveness
• Always ensure compliance with user consent and messaging regulations

Best Practice Recommendation #

For secure and scalable applications:

✔ Use OAuth 2.0 (Bearer Token)
✔ Send Flash SMS if only needed
✔ Avoid exposing API tokens in URLs
✔ Always use HTTPS

Summary #

Sending Flash SMS via Text.lk is simple. Just add: “is_flash”: true to your existing SMS API request, and your message will be delivered as a high-priority flash message.

👉 See also: How to send SMS via Text.lk API
👉 See also: API authentication methods