Similar to your previous node, try passing a reference to the @pkg array:

XRC::changePkg( $username, \@pkg );
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I still don't have access to the required wsdl file, so it's a bit of a guess, but here's what SOAP::Lite generates for the array without the wsdl:

<soapenc:Array soapenc:arrayType="xsd:int[1]" xsi:type="soapenc:Array"
+>
      <item xsi:type="xsd:int">5544</item>
</soapenc:Array>
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I think you'll find it'll turn out alright when the wsdl is in place.