这可能是由于密钥或日期不正确导致的。请确保使用正确的密钥和日期生成签名。另外，还要检查所选的区域是否正确，并确保使用正确的HTTP方法（如GET或POST）和端点。

下面是一个示例代码，用于实现AWS SigV4签名，并避免出现此问题：

import hashlib
import hmac
import datetime
import requests

# AWS认证信息
access_key = 'YOUR_ACCESS_KEY_ID'
secret_key = 'YOUR_SECRET_ACCESS_KEY'

# AWS区域信息
region = 'YOUR_AWS_REGION'
service = 's3'

# HTTP请求信息
url = 'https://s3.amazonaws.com/YOUR_BUCKET_NAME/YOUR_FILE_NAME'
method = 'GET'

# 生成签名
def sign(key, msg):
    return hmac.new(key, msg.encode('utf-8'), hashlib.sha256).digest()

def getSignatureKey(key, dateStamp, regionName, serviceName):
    kDate = sign(('AWS4' + key).encode('utf-8'), dateStamp)
    kRegion = sign(kDate, regionName)
    kService = sign(kRegion, serviceName)
    kSigning = sign(kService, 'aws4_request')
    return kSigning

def get_signed_url(url):
    # 生成时间戳和日期字符串
    t = datetime.datetime.utcnow()
    amz_date = t.strftime('%Y%m%dT%H%M%SZ')
    datestamp = t.strftime('%Y%m%d')

    # 构造认证信息
    canonical_uri = '/'
    canonical_querystring = ''
    canonical_headers = 'host:' + service + '.' + region + '.amazonaws.com\nx-amz-date:' + amz_date + '\n'
    signed_headers = 'host;x-amz-date'
    payload_hash = hashlib.sha256(('').encode('utf-8')).hexdigest()
    canonical_request = method + '\n' + canonical_uri + '\n' + canonical_querystring + '\n' + canonical_headers + '\n' + signed_headers + '\n' + payload_hash
    algorithm = 'AWS4-HMAC-SHA256'