Tax reclamation on SIPP. Really need advice.

Hi, please be gentle as I'm very anxious. On 4th April 2023 I made a sipp contribution. The funds cleared on 5th April in their accounts. As it missed their 31st March deadline they allocated it to 23/24 tax year. I have claimed tax relief in 22/23 personal tax return as my accountant said I had paid it (and they had received) it in 22/23. But they refuse to budge on the year of allocation. What can I do? Does the pension year they have allocated it to set the year i should reclaim tax, or do accountant rules apply because I paid it in 22/23? Whilst I understand I missed their deadline my understanding is that guidance is to ensure money is cleared by the end of the tax year to avoid disputes about money sent pre 5th April arriving post 5th April and arguing about who was right/ wrong. Every other accounting rule i have seen is dictated by when money is sent/received, not when it is allocated. Any help gratefully received.

Hi Granitas Black,
HMRC considers the date of receipt, based on the method of payment.
Please have a look here:
PTM041000 - Contributions: essential principles,
To help you work out which tax year the payment should be declared.
Thank you.