javascript
// Example with Express.js
const express = require('express');
const app = express();
app.use(express.json());

app.post('/vapi-webhook', async (req, res) => {
  // The webhook payload contains information about the incoming call
  const { message } = req.body;
  
  if (message.type === 'assistant-request') {
    try {
      // Extract the caller's phone number
      const callerNumber = message.customer?.number;
      
      if (!callerNumber) {
        return res.json({
          messageResponse: {
            assistantId: "YOUR_ASSISTANT_ID", // Your existing assistant ID
            error: null
          }
        });
      }
      
      // Fetch customer data from your database using the caller's number
      const customerData = await fetchCustomerData(callerNumber);
      
      // Return the assistant configuration with customer data as variables
      return res.json({
        messageResponse: {
          assistantId: "YOUR_ASSISTANT_ID", // Your existing assistant ID
          assistantOverrides: {
            variableValues: {
              // Add all your fetched customer data as variables
              customer_name: customerData.name,
              customer_plan: customerData.plan,
              customer_status: customerData.status,
              // Add any other relevant customer data
              is_premium: customerData.isPremium,
              last_interaction: customerData.lastInteraction
            }
          }
        }
      });
    } catch (error) {
      console.error('Error fetching customer data:', error);
      // If there's an error, still proceed with the call but without custom data
      return res.json({
        messageResponse: {
          assistantId: "YOUR_ASSISTANT_ID"
        }
      });
    }
  }
  
  // Handle other webhook types if needed
  res.json({ messageResponse: {} });
});

// Function to fetch customer data from your database
async function fetchCustomerData(phoneNumber) {
  // Implement your database query here
  // Return customer data object
}

app.listen(3000, () => {
  console.log('Webhook server running on port 3000');
});

You are a helpful customer service agent for {{company_name}}.

Customer Information:
- Name: {{customer_name}}
- Plan: {{customer_plan}}
- Status: {{customer_status}}
- Premium Customer: {{is_premium}}
- Last Interaction: {{last_interaction}}

Use this information to provide personalized service, but don't explicitly tell 
the customer you have this data unless they ask for confirmation.