Retentions not carried out by payer imputed to the period of rental imputation

A professional asks whether retentions on 2023 invoices, not carried out by the payer, can be deducted and corrected by a new payment in 2024. The DGT responds that retentions must be imputed to the period in which the income is imputed, and if the failure to withhold is the payer's fault, the professional may deduct the amount that should have been withheld.