What is web service Url:

A web service is a web application which is basically a class consisting of methods that could be used by other applications. It also follows a code-behind architecture such as the ASP.NET web pages, although it does not have a user interface.
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To create web service Url for Attachments.expert® application please go through the below article:

Link: https://orektic.freshdesk.com/solution/articles/3000058762-install-attachments-expert-on-your-own-server
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Note :When user will Browse Attachments.expert® application, then it will redirect to application's login page. Copy the generated Url mentioned in the login page and use that URL for Local, FTP and SFTP storage server.