In addition to creating web services for SharePoint on-premise it is also possible to create web services for Office 365/SharePoint Online in the WebService Designer.

You can use the Call Web Service workflow action in Nintex Workflow for Office 365 to call SAP integrated REST web services.

Important: The prerequisite for that functionality is an installation of Theobald Software component ECS Core. Detailed information about ECS Core can be found here.

Create a web service for ECS Core

Create a Nintex Workflow for Office 365

Test the workflow