What does the cryptic crossword clue "This may be required to enter an empty ground (7)" mean?

The definition is "This". The wordplay uses an anagram. anagram of AN + EMPTY = PAYMENT; definition: "This" The answer is PAYMENT.

This may be required to enter an empty ground (7)

Guardian Cryptic #29264 | 23 Across | 2023-12-28 flower