Use OneSignal to notify users about social activity (likes, follows, invites) and user messages. These alerts can drive re-engagement even when users aren’t currently active in your app.
OneSignal and push notifications are not designed explicitly for real-time communication. They are best used as a fallback when both users are not active on your app.For real-time communication, consider dedicated live chat solutions such as:

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Social activity notifications

Trigger a push notification when a user is involved in social actions.

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Common social actions

ActionExample message
Like“Anna liked your post.”
Mention“Leo mentioned you in a comment.”
Tag“Sara tagged you in a photo.”
Invite“Ben invited you to the event.”
Comment“Maya replied: ‘Looks awesome!’”
Follow“James started following you.”
Share“Alex shared ‘Hawaii Album’ with you.”

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Requirements

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Setup

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1. Map users with External ID

Use Aliases & External ID to uniquely identify users in OneSignal.

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2. Detect the social action

In your backend, track who performed the action and who it affects.
json
{
  "action": "like",
  "actor_id": "user_b",
  "recipient_id": "user_a",
  "post_id": "xyz789"
}

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3. Send a push notification

Use the OneSignal API to notify the recipient: 
{
  "app_id": "YOUR_APP_ID",
  "contents": { "en": "user_b liked your photo." },
  "include_aliases": { "external_id": ["user_a"] }
}

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Add-ons

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Direct (user-to-user) messages

Let users know they have a new message and optionally include message content or a deep link to the chat.
Push notifications are best used as a fallback when both users are not actively chatting in the app.
Send a push when User A sends a message to User B, and B is not currently online or in the chat screen.

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Setup

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1. Map users with External ID

Use Aliases & External ID to uniquely identify users in OneSignal.

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2. Trigger a notification on message send

From your backend, send a push to the recipient using the Create Notification API with the include_aliases field: 
{
  "include_aliases": {
    "external_id": ["USER_B_ID"]
  },
  "contents": { "en": "New message from Anna: 'Hey, you around?'" },
  "headings": { "en": "New Message" },
  "data": {
    "sender_id": "user_a",
    "conversation_id": "chat_1234",
    "click_action": "open_chat"
  }
}

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Best practices

  • Avoid spamming: Don’t send a notification for every single message. Use batching or only alert after X minutes of inactivity.
  • Respect user settings: Let users mute or disable message notifications if needed.
  • Use routing logic in your app to open the conversation. See Deep Linking for more information.