The configuration as described in https://community.jaspersoft.com/wiki/installing-webservice-datasource causes the application not starting for Jasper Server 7.1.
Many of the capabilities of the webservice plug-in are now part of the data adapters, I think for CSV, XML, and JSON file formats. There is an example of how to configure and use a webservice data adapter directly in JSS here:
The webservice data source you linked to is a plug-in and not part of the main development of JSS. The people who created would only have gotten access to JSS 7.1 when it was released. They may plan to update the plug-in, but would not have had time to do it yet.