The SOAP action field is mandatory in BW. It can be set to blank in the BW SOAP and Service palette. This means that the client still needs to set the SOAP action header with an empty value when it calls a BW service. BW automatically generates a value for the SOAP action field. You can manually remove the generated value and set it to blank. You will find the SOAP action field when you click on the service -> Endpoint Bindings -> SOAP details.