Classic template should display error messages

[pauloiankoski]

Details

Currently, the Classic template does not display error messages. When you submit a donation form and there's an error while processing the form, nothing is returned.

Expected Behavior

Whenever you have an error, it must be printed on the form so the user is aware something happened with the transaction.

Steps to Reproduce

The following steps are only one example of how to trigger an error.

1. Create a form that accepts recurring payments
2. Select the Classic Template
3. Go to the page with that form
4. Select the option to pay recurrently
5. Select Offline Payment as the method (it does not support recurring payments)
6. Submit the form and see that nothing happens

Visuals

Multi-step form presenting the error message

Classic template form with no error message

Return of the ajax call

Acceptance Criteria

• [x] When the form submission responds with an error, it's printed out.

[JasonTheAdams]

This is merged so we can't link it, but here's the Canny post this belongs to: https://feedback.givewp.com/bug-reports/p/classic-template-does-not-display-error-messages