If the party that publishes the service needs the element in the request to be in a specific order that should be reflected in the wsdl. Based on your question I don't think that they have a fixed sequence in their wsdl or that the sequence is specified incorrect.
In the wsdl you should see the definition of these elements. It should be specified similar to below, the xs:sequence tells the platform to follow the specified fixed order. And will export all elements in sequence as they are specified.
<xs:element name="OpportunityManagement">
<xs:complexType>
<xs:sequence>
<xs:element name="AmountRequested" type="xs:string"/>
<xs:element name="Description" type="xs:string"/>
<xs:element name="EstCloseDate" type="xs:string"/>
</xs:sequence>
</xs:complexType>
</xs:element> <AmountRequested>275000</>
Since the platform literally follows the wsdl spec I would recommend downloading the wsdl and changing this to the correct sequence. If you want a more detailed suggestion, you could try adding the wsdl to your question.