What does the cryptic crossword clue "Assess as having no VAT to pay, nothing to reprove (4-4)" mean?

The wordplay uses a charade (building blocks). ZERO (synonym="nothing") + RATE (synonym="reprove") = ZERORATE The answer is ZERORATE.

Assess as having no VAT to pay, nothing to reprove (4-4)

Guardian Cryptic #29016 | 8 Across | 2023-03-13 flower