Steps to reproduce

• Request the donation form using the skin 10h16 (https://test-spenden.wikimedia.de/?skin=1).
• Select any amount option.
• Select any payment method.

Expected Result

• The input validation passes, clicking the submit button leads to the second form page.

Actual Result

• The custom amount field gets a red border indicating that the donation amount is invalid.
• When clicking the submit button, a red box is displayed above the form containing an error message related to the donation amount.

Notes

• Apparently, this was introduced with T210162.
• This happens only on test-spenden, not on test-spenden-2.
• The client calls validate-donation-amount, which returns:

{
  status: "ERR",
  messages: {
    amount: "Amount must be in cents."
  }
}