Paypal自适应支付PHP Soap SDK未定义定义

我正在尝试将自适应支付系统集成到centos服务器上的codeigniter项目中。SOAP安装在我的服务器上（我通过ssh执行了“yum install php SOAP”并重新启动了服务器），当我尝试运行时，会出现如下错误：

A PHP Error was encountered
Severity: Notice
Message: Use of undefined constant XML_SERIALIZER_OPTION_INDENT - assumed 'XML_SERIALIZER_OPTION_INDENT'
Filename: SOAPEncoder/SOAPEncoder.php
Line Number: 41
A PHP Error was encountered
Severity: Notice
Message: Use of undefined constant XML_SERIALIZER_OPTION_INDENT - assumed 'XML_SERIALIZER_OPTION_INDENT'
Filename: SOAPEncoder/SOAPEncoder.php
Line Number: 41

我遗漏了什么，我该如何解决

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谢谢，

也许您需要安装XML\u序列化程序PEAR包：

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很抱歉回复晚了，我生病了。。。是的，这就是问题所在，谢谢！

pear install XML_Serializer