Your must amend the browser URL in order for it to authenticate properly.
There could be three reasons to this:
1. Shortened URL
For example, if you enter the following URL in the Add Site dialog: http://sitename.corporate.local/subsite/SitePages/Home.aspx, Briefcase is able to detect the root of the site for authentication. However, if you turn this URL into a shortened one, Briefcase is no longer able to detect the root and authentication will fail. Therefore if you want to create a shortened URL, you must amend the original URL to read as follows: http://sitename.corporate.local/subsite/
2. Site Resolution
iPads do not behave the same way as PCs do on a network, and as such iPads do not resolve URLs the same way as PCs. This may result in an error when adding a site to the Sites list in Briefcase.
Resolution:
The SharePoint site should have the fully qualified URL added to the access modifiers.
For example: http://pacificfinancial/Pages may need to be entered as http://pacificfinancial/Pages.corporate.local
3.Site is not connectable
Contributor was able to connect to a web server but the SharePoint site with the specified URL was not found on this server.
Resolution:
Ensure the site exists and that you have at least read permissions.