"INVALID_CONTENT_HASH"错误是由于Bittrex REST API v3将HTTP请求的内容哈希与提供的签名不匹配引起的。以下是解决方法的代码示例：

import requests
import hmac
import hashlib
import time
import json

api_key = 'YOUR_API_KEY'
api_secret = 'YOUR_API_SECRET'
base_url = 'https://api.bittrex.com/v3'

def generate_signature(url, method, content_hash, timestamp):
    message = url + method + timestamp + content_hash
    signature = hmac.new(api_secret.encode(), message.encode(), hashlib.sha512).hexdigest()
    return signature

def post_order(market, side, quantity, price):
    endpoint = '/orders'
    url = base_url + endpoint

    # 构建请求体
    body = {
        'marketSymbol': market,
        'direction': side,
        'type': 'LIMIT',
        'quantity': str(quantity),
        'limit': str(price),
        'timeInForce': 'GOOD_TIL_CANCELLED'
    }

    # 将请求体转换为JSON字符串
    json_body = json.dumps(body)

    # 获取当前时间戳
    timestamp = str(int(time.time() * 1000))

    # 计算请求体的SHA-512哈希
    content_hash = hashlib.sha512(json_body.encode()).hexdigest()

    # 生成签名
    signature = generate_signature(endpoint, 'POST', content_hash, timestamp)

    # 发送POST请求
    headers = {
        'Api-Key': api_key,
        'Content-Type': 'application/json',
        'Content-Length': str(len(json_body)),
        'Bittrex-Content-Hash': content_hash,
        'Bittrex-Api-Key': api_key,
        'Bittrex-Timestamp': timestamp,
        'Bittrex-Signature': signature
    }

    response = requests.post(url, headers=headers, data=json_body)
    print(response.json())

# 调用函数提交订单
post_order('BTC-USDT', 'BUY', 0.001, 35000)

请确保替换YOUR_API_KEY和YOUR_API_SECRET为您的Bittrex API密钥。此示例中的post_order函数使用requests库发送POST请求，构建请求头，计算内容哈希和签名。