noun
omission in a bill; item left off a check
Refers to an item or charge that was accidentally or intentionally left out of a bill or account, especially in restaurant or commercial contexts.
レジで付け落としが見つかって、追加で支払った。
An omission in the bill was found at the register, and I paid the extra amount.
会計のとき、付け落としがないか確認してください。
When settling the bill, please check that nothing has been left off.
付け is a bill or account; 付け落とし specifically refers to an item omitted from such a bill.
落とし means omission or dropping; combined with 付け it forms the compound meaning 'bill omission'.
Compound of 付け (bill, account) and 落とし (omission, dropping). The exact historical derivation is uncertain, but the word transparently describes an item left off a bill.