Question 9 - What is the time of supply applicable with regard to addition in the value by way of interest, late fee or penalty or any delayed payment of consideration?

Time of supply: receipt by the supplier fixes tax point for interest, late fees or penalty on delayed payment.

The time of supply for additions to taxable value due to interest, late fee, penalty, or delayed consideration is the date on which the supplier receives that additional consideration, so receipt constitutes the tax point for those adjustment items.