Here is a working example based on this...
flow...
result...
export of the flow i used
[{"id":"6e215f49.aadfe","type":"inject","z":"68fd4d54.10dd54","name":"","topic":"","payload":"","payloadType":"date","repeat":"","crontab":"","once":false,"onceDelay":0.1,"x":260,"y":400,"wires":[["261bcfb3.22dac"]]},{"id":"261bcfb3.22dac","type":"change","z":"68fd4d54.10dd54","name":"","rules":[{"t":"set","p":"headers","pt":"msg","to":"{}","tot":"json"},{"t":"set","p":"headers['SOAPAction']","pt":"msg","to":"https://www.w3schools.com/xml/FahrenheitToCelsius","tot":"str"},{"t":"set","p":"headers['Content-Type']","pt":"msg","to":"text/xml","tot":"str"},{"t":"set","p":"payload","pt":"msg","to":"<?xml version=\"1.0\" encoding=\"utf-8\"?> <soap:Envelope xmlns:xsi=\"http://www.w3.org/2001/XMLSchema-instance\" xmlns:xsd=\"http://www.w3.org/2001/XMLSchema\" xmlns:soap=\"http://schemas.xmlsoap.org/soap/envelope/\"> <soap:Body> <FahrenheitToCelsius xmlns=\"https://www.w3schools.com/xml/\"> <Fahrenheit>100</Fahrenheit> </FahrenheitToCelsius> </soap:Body> </soap:Envelope>","tot":"str"}],"action":"","property":"","from":"","to":"","reg":false,"x":420,"y":400,"wires":[["2bd2ae1f.24ec22"]]},{"id":"2bd2ae1f.24ec22","type":"http request","z":"68fd4d54.10dd54","name":"","method":"POST","ret":"txt","paytoqs":false,"url":"https://www.w3schools.com/xml/tempconvert.asmx","tls":"","persist":false,"proxy":"","authType":"","x":610,"y":400,"wires":[["543921d8.c6caa"]]},{"id":"41fb1ba0.9393f4","type":"debug","z":"68fd4d54.10dd54","name":"","active":true,"tosidebar":true,"console":false,"tostatus":false,"complete":"true","targetType":"full","x":890,"y":400,"wires":[]},{"id":"543921d8.c6caa","type":"xml","z":"68fd4d54.10dd54","name":"","property":"payload","attr":"","chr":"","x":770,"y":400,"wires":[["41fb1ba0.9393f4"]]},{"id":"1ca55c6.5df13a4","type":"comment","z":"68fd4d54.10dd54","name":"Send 100 deg Fahrenheit to tempconvert.asmx for conversion to Celcius (SOAP POST, XML Result)","info":"","x":540,"y":360,"wires":[]}]