is it possible to start process instance by a wasdl call ?
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Information on how to publish a process model as a web service is here: https://docs.appian.com/suite/help/19.3/Publishing_Process_Models_as_Web_Services.html
Also note that the above approach is somewhat dated. Currently, it's recommended to use Appian Web API's.https://docs.appian.com/suite/help/19.3/Web_APIs.html