the expiry of a fixed-term contract定期合同的到期

the expiry of a lease租约的满期

You will have to purchase top-up vouchers to keep the SIM active, and the calling credit has set expiry periods.你需要购买充值卡充值才能保证SIM卡处于激活状态, 此外, 呼叫余额是设定了有效期限的。