Future year earn out payments from company sale, how to report in self-assessment

Hello, in 2020/2021 tax year our company was bought out, and so as part of a share purchase agreement, we had known payouts + 3 years of earn out payments as deferred considerations. Lets just say they are: £100k known payouts for sale £25k estimated year 1 earnout £25k estimated year 2 earnout £25k estimated year 3 earnout For CGT purposes they are all considered as part of the disposal in Dec 2020 even though earn out figures not known at the time. So initially in the 2020/2021 self assessment, I declared the total figure of £175k including both ascertainable and unascertainable estimates for earnouts. When the 1st earnout was made I just amended the initial 2020/2021 disposal proceeds amount to reflect. However the year 2 earnout was lower than expected e.g. £20k instead of £25k. How do I correctly report in the self assessment tax return in this situation? Do I add a new disposal for the second earnout in with value of £20k with a deduction of £25k which then shows a loss of £5k, but then this loss does not appear to be included in any calculations to receive overpaid tax back from 2020/2021. I couldn't find clear guidance on this scenario, and specifically how to address this on self-assessment. Many thanks for any help / pointers, I hope the above makes sense!

(and to clarify, shares did not have voting rights, so no entrepreneurs relief / BADR considerations)

Hi TaxMoo,
You may wish to consider making a S48 claim
Please have a look at CG14933 - Deferred consideration: ascertainable: claims that consideration is irrecoverable.
CG14933 - Deferred consideration: ascertainable: claims that consideration is irrecoverable
And:
CG15080 - Deferred consideration: unascertainable: election for treatment of loss:
CG15080 - Deferred consideration: unascertainable: election for treatment of loss - introduction
Thank you.