1. 确认本地moto服务器是否已经启动，并且端口号是否正确。

2. 确认boto3中cognito-idp的配置是否正确，包括Region、AccessKey、SecretKey等信息。

示例代码：

import boto3
from botocore.config import Config
from botocore.exceptions import ClientError
from awscli.customizations import configure

config = Config(region_name='us-east-1')
client = boto3.client('cognito-idp', config=config, aws_access_key_id='YOUR_ACCESS_KEY',
                      aws_secret_access_key='YOUR_SECRET_KEY')

try:
    response = client.admin_get_user(
        UserPoolId='YOUR_USER_POOL_ID',
        Username='USERNAME'
    )
    print(response)
except ClientError as e:
    print(e)