from datetime import datetime

def revenue_counts_by_day(data):
    revenue_counts_by_day = {}

    for rev in data.get("data", []):
        order_created_at = rev.get('orderCreatedAt')
        timestamp_s = order_created_at / 1000
        dt = datetime.fromtimestamp(timestamp_s)
        date_str = dt.strftime('%Y-%m-%d')
        
        order_subtotal = rev['data'][0]['order']['details'].get('order_total')
        order_subtotal = float(order_subtotal) if order_subtotal is not None else 0.0  # Ensure order_subtotal is a float
        
        if date_str in revenue_counts_by_day:
            revenue_counts_by_day[date_str] += order_subtotal
        else:
            revenue_counts_by_day[date_str] = order_subtotal

    return revenue_counts_by_day