How to pay voluntary NI gaps online

I'd like to pay for 5 incomplete years of NI contributions before the deadline on 5th April. I'm 40 years old so i understand i don't necessarily need to do this at this stage as i should still be able to work enough years from now until i retire to make up my 35 years NI and be eligible to receive the full state pension. However, id like to pay them anyway. I've been onto my tax/NI account where it tells me about incomplete NI years etc, but the only way i can pay for these gap years online is to put in a random date like 2035 into the section "when do you plan to stop paying national insurance contributions". Does this date matter in the grand scheme? If i type a later date, it wont let me purchase all 5 years. Later on in the process, it asks me if i can confirm that I've been truthful with all of the information I've provided. I am only typing in 2035 so i can pay for the full 5 extra years online. Can someone clarify this for me ASAP please? Many thanks.

Can anyone help with this ASAP please as the deadline is fast approaching. Thanks.

Hi _viator,
The system seems to be assuming that you will be earning enough contributions when typing in a later date and may not need to make contributions.
As this is based on a pension calculation you will benefit from discussing with the Future Pension Service about how making contributions will benefit your pension before making payments.
You can contact them on 0800 731 0175 
A high number of calls to the helpline is resulting in long wait times, you can complete a call back request form on the gov.uk if this is affecting you. 
You can complete this form if you're struggling to contact the Department for Work and Pensions (DWP) by phone to pay voluntary National Insurance Contributions.
DWP will contact you on the phone number you provide in this form to discuss payment of voluntary National Insurance contributions.
If you submit a request by the 5 April 2025 deadline, you will still be able to pay voluntary National Insurance contributions after the deadline has passed.
If you have already requested a call back, please do not send another request.
You can fill in the form following this link
Request a call back to pay voluntary National Insurance contributions