You will need:
WhatsApp only allows proactively sending messages if they’re created from a template. You can create a template from your WhatsApp Manager dashboard.After WhatsApp reviews and approves your template, follow the steps in this guide.

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Setup

1

Add the Start Conversation Card

In Studio, add a Start Conversation Card to any Node:Start Conversation
2

Fill in the required fields

Fill in the fields:
Your bot is ready to proactively start a conversation with your user!

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Access the Conversation ID

You can access the proactively started conversation’s ID in Studio by storing the Start Conversation Card’s output in a variable. Just select a variable to store the value in: Output Value field The output value of this action will be an object with the following structure: 
{
  conversationId: 'xxxxxxxxxxxxxxxxxxxxx'
}

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Create the conversation from code

You can also call actions.whatsapp.startConversation in an Execute Code Card to start a conversation: 
actions.whatsapp.startConversation({
  conversation: {
    userPhone: '+1 123 456 7890',
    templateName: 'test_message',
    templateLanguage: 'en',
    templateVariablesJson: JSON.stringify(['First value', 'Second value'])
  }
})