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は用意できた

… is ready

→ は
phrase Rare #34,471
… is ready は marks what is being discussed. 用意できた means it was successfully prepared, so in questions it often asks whether something is ready.
JA: 必要な書類は用意できた。
EN: I got the necessary documents ready.

武器は用意できたぞ

I’ve got the weapons ready.

— RRR (2022)

パスポートは用意できた

I've got my passport ready.

— Брат 2 (2000)

金は用意できたか？

Were you able to get the money ready?

— イップ・マン 序章 (2008)

ケーキは用意できた？

Were you able to get the cake ready?