Voluntary national insurance contributions and state pension

Hi there. My friend reached state pension age on 9 March 2023 and the letter from DWP says that she had 45 State Pension qualifying years. She is not receiving the full amount of state pension as HMRC have indicated that she can pay for an additional 3 years to receive the maximum amount of State pension. I have calculated that if she pays the 3 years additional contributions - totalling £2,420.60 she should receive the full amount of the state pension but before she pays it I just want it clarified that the full amount will then be received. 2nd question though - can you please advise as to why if she had 45 State Pension qualifying years she isn't entitled to the full state pension now before paying the voluntary contributions for the 3 additional years. The deficient years are 2017-2018 through to 2020-2021. She stopped working on 7th November 2016. Many thanks for your help

Hi Joanne,
Thank you for your query.
Please contact the Future Pensions Centre at the Department for Work and Pensions if you would like confirmation of what the increase of your friends state pension will be after making a voluntary payment. HMRC cannot confirm this information.  Please find the contact details below:
Number 0800 731 0175
Text Relay: 18001 0800 731 0176
+44 191 218 2051
Welsh 0800 731 0453
Overseas +44 191 218 3600
Address
The Pension Service 9
Mail Handling Site A
Wolverhampton
WV98 1LU
United Kingdom
Open: 8.00am to 6.00pm Monday to Friday
Web Address
Contact the Future Pension Centre
Your friend has more than likely been contracted out of the State pension at some point during their working life. This is normally the reason why somebody would need more than 35 qualifying years to get the maximum State pension,