Why is there no failed donation page?
All the fields get immediately validated (if the email field really got an email address and if IBAN, credit card,.. have the right format and digits). Then the payment gets to the payment processor. Which is either stripe or if manual whoever processes the data. Most payment providers don't give any feedback if the payment worked to the site, if it worked or not, it just redirects back (or displays its own "failed donation" page). Manual direct debit, too, we can't look into account information and it would also take to long for Campaignion to wait, so we just save the supporter data and carry on.