curl -X POST "https://server.smartlead.ai/api/v1/campaigns/123/message-history-for-leads/bbfbdsFGHlBr76ruhjvh6fhHL?api_key=YOUR_KEY" \
  -H "Content-Type: application/json" \
  -d '{"lead_ids": [789, 790, 791]}'

import requests

def get_bulk_lead_history(campaign_id, lead_ids=None):
    payload = {"lead_ids": lead_ids}
    
    response = requests.post(
        f"https://server.smartlead.ai/api/v1/campaigns/{campaign_id}/message-history-for-leads/bbfbdsFGHlBr76ruhjvh6fhHL",
        params={"api_key": "YOUR_API_KEY"},
        json=payload
    )
    
    return response.json()

# Get history for specific leads
history = get_bulk_lead_history(123, [789, 790, 791])

# Get history for all leads (pass null)
all_history = get_bulk_lead_history(123, None)

{
  "data": {
    "789": [
      {"subject": "Email 1", "sent_at": "2025-01-15T10:00:00Z"}
    ],
    "790": [
      {"subject": "Email 1", "sent_at": "2025-01-15T10:05:00Z"}
    ]
  }
}