Yes, you can set a custom URL for donors to get redirected to after they've donated!
Click on the Edit button, under your Campaign name. On the next page, look for the Technical Section and click on "Tracking":
Toggle on the Redirection section, labeled "Redirect to a custom URL after donation". A text box will appear for you to add the URL that you want donors to be taken to after they've donated - as shown below.
Once you add your URL, hit "Update" and you are all set. Please ensure the URL you add is a valid link, or else donors may think that your donation form is faulty.
Please note that the following section is only available with Donorbox Premium.