Lorena, the 403 error usually means that there is no file designated to be displayed at the location you are going to. The link does not include a file at the end, but all websites have a default setting for the name of the file to be displayed when it is not specified. Therefore, the most likely cause of the error is that whatever default file is specified does not exist in the root folder of that website.
Another possible cause would be that there is a file there that can be displayed, but its name is not the default so it has to be included at the end of the link.
I think the reason it is labeled "forbidden" is that if no default display file exists the browser would like to display the directory listing of the root folder of the website. This is generally never permitted by web servers, mainly for privacy and security protections.