🔄 expire vs invalid

合約「過期」了，應該說 expired 還是 invalid？

📖 解釋

expire → 指有效期限結束，不再有效。
👉 My passport expired last month.

invalid → 指「無效、不合法」，可能從一開始就錯誤。
👉 The contract was invalid because it wasn’t signed.

✅ 小測驗
Which is correct?
“The coupon will ___ after July 31st.”
👉 expire