When this happens, your donor is probably attempting to process a credit card donation on your donation form and you have not connected a Stripe account to Donorbox. If you have not connected to a Stripe or a PayPal account, the form won't work.
To sign up for Stripe, go to your Payment Processors page and click the "Create your Stripe account" button. If you already have a Stripe account, you can click "Already have a Stripe account?" to connect it to Donorbox.
For more information on how to get started with Donorbox, feel free to check out our blog.