What does the cryptic crossword clue "A herald's goofed badly to promote a lost cause? (4,1,4,5)" mean?

The wordplay uses an anagram. anagram of A + HERALD'S + GOOFED = FLOGADEADHORSE The answer is FLOGADEADHORSE.

A herald's goofed badly to promote a lost cause? (4,1,4,5)

Daily Mail Cryptic #16978 | 26 Across | 2022-11-29 flower