Sumarokov Elston

I am experiencing a problem trying to make a payment. When I try to pay either my voluntary Class 3 or Class 2 contributions using "your ’18 Digit Reference Number’ is your National Insurance Number IC surname and initial (or as much of your surname as possible)", I get the following message in red: https://www.tax.service.gov.uk/pay/enter-class-3-national-insurance-reference?traceId=80913927 There is a problem Enter your Class 3 National Insurance reference number in the correct format What is your Class 3 National Insurance reference number? This is 18 digits and begins with 60. For example, 603490017829614130. You’ll find it on your payment request, or you can request an 18-digit reference number from the National Insurance helpline. Enter your Class 3 National Insurance reference number in the correct format The system seems to refuse to accept an ’18 Digit Reference Number’ that is a National Insurance Number IC surname and initial. Am I doing something wrong? Am I following the wrong link? I went to the following page and clicked on the green "Pay now" button: https://www.gov.uk/pay-voluntary-class-3-national-insurance/pay-online-using-bank-account