Sample XML for https://github.com/skyverge/woocommerce-xml-rpc-api

gistfile1.xml

<methodCall>
  <methodName>
	wc.updateOrderStatus  
	</methodName>
	<params>
		<param>
			<value>
				<struct>
					<member>
						<name>username</name>
						<value>
							<string>your_wp_username</string>
						</value>
					</member>
					<member>
						<name>password</name>
						<value>
							<string>your_wp_password</string>
						</value>
					</member>
					<member>
						<name>order_status</name>
						<value>
							<string>completed</string>
						</value>
					</member>
					<member>
						<name>order_number</name>
						<value>
							<string>1234</string>
						</value>
					</member>
				</struct>
			</value>
		</param>
	</params>
</methodCall>