我正在尝试通过JavaPayPalSDK连接到我的paypal业务帐户，以自动发送发票。我将.properties文件配置为：

http.ConnectionTimeOut=5000
http.Retry=1
http.ReadTimeOut=30000
http.MaxConnection=100

# HTTP Proxy configuration

# If you are using proxy set http.UseProxy to true and replace the following

values with your proxy parameters
http.ProxyPort=8080
http.ProxyHost=127.0.0.1
http.UseProxy=false
http.ProxyUserName=null
http.ProxyPassword=null

# Set this property to true if you are using the PayPal SDK within a Google

App Engine java app
http.GoogleAppEngine = false

# Service Configuration

service.EndPoint=https://api.sandbox.paypal.com

# Live EndPoint

# service.EndPoint=https://api.paypal.com

# Credentials

clientId=ID (of SANDBOX API CREDENTIALS)
clientSecret=SECRET (of SANDBOX API CREDENTIALS)

# Webhook Validation

# webhook.trustCert=DigiCertSHA2ExtendedValidationServerCA.crt

当它连接时，我得到“错误消息：应用程序属性中没有配置api帐户”。我的.properties文件有什么问题？