Namespace value in SOAPAction does not match Namespace value 'http://schemas.xmlsoap.org/soap/envelope/' in xml tag 'Body'

This issue normally comes when we use Service Callout.

Service Callout has an option to  configure Body or Payload

Payload means , it will be send as a child of Body.

If you pass your request which is already a SOAP Body as a payload,  and if you select Payload Document Option it will be like sending a SOAP Body inside SOAP Body. That might result the above error.

In such cases choose wisely which option you need to select while sending request via service callout

If your request itself is a SOAPBody choose the SOAP Body option. Otherwise choose the payload option