Postponed VAT Accounting was introduced in January 2021 to allow UK VAT registered importers to account for and recover import VAT on the same VAT return, subject to the normal rules on import tax deduction.
Essentially, rather than pay import VAT when your goods are imported into the UK, and then reclaim the VAT on your VAT return, PVA allows you to both declare and reclaim the import VAT on your VAT return. Meaning no cash is transferred and your VAT liability is neutral (as the amount you pay is offset by the amount you reclaim).
For further information, please refer to GOV.UK.