Sometimes visitors may make their way to a url on your subdomain that doesn't have a page (donate.yourcause.com). It's usually because a page was unpublished or invalid. It's always good to make sure a donor always lands safely on a donation page when you can. Revv's Default page feature lets you set a page that visitors are directed to when they manually type in your plain subdomain or navigate to a page that doesn't exist.
To set a default page, go to your Revv settings and click Pages. Under Default page, select one of the pages you've already published to set it as default. If you haven't published any pages, this feature won't work.