What does the cryptic crossword clue "Chain's not prepared to supply upright post (9)" mean?

The definition is "post". The wordplay uses an anagram. anagram of CHAIN'S + NOT = STANCHION; definition: "post" The answer is STANCHION.

Chain's not prepared to supply upright post (9)

Daily Mail Cryptic #17300 | 14 Down | 2024-02-23 flower