https://www.slab.org.uk/faqs/payments-of-your-account/
If you have submitted an interim or final claim in respect of solicitors fees and outlays for a client who has no right to stay in the UK and this has been paid with VAT, we do not propose to take steps to recover those sums on the basis that we expect the VAT element to have been accounted for to HMRC, in the normal manner.
All accounts in respect of solicitors fees and outlays paid on or after 23 September 2023 will be paid as VAT exempt where it is confirmed, or established, that the legal services were provided to a client who has no right to stay in the UK.
This includes any case where previous payment(s) inclusive of VAT has been paid in that case.
Any subsequent payments on or after 23 September 2023 will be paid as VAT exempt so it is possible you may have some cases which have been treated differently for the purposes of VAT.