Ar ôl is-adran (6A), mewnosoder—

“(6B)

A decision under subsection (3) by a billing authority in Wales is invalid as regards a day if—

(a)

the day falls before the end of the financial year beginning on 1 April 2023, and

(b)

the decision is made more than six months after the end of the financial year in which the day falls.”