How do I set up the thank you page for Fundraiser?

I cannot seem to figure out how to get the thank you page to work. I keep getting a 404 message

The plugin works fine and receives donations perfectly. It's only the thank you page that is goofy. I'm presently using woo commerce and am afraid to point the ipn in paypal to the page your plugin says to just in case it breaks the online store. The online store is more important than the donation page but both are necessary.

I look forward to getting a response. Thank you and have a great day