翻译：您必须先付定金，款到付货

这句话本身就有漏洞。这样做外贸要吃亏滴。
款到付货中的款是指定金呢？还是全额？
We shall deliver the goods after getting XX percent deposit.
这是按你的原话翻译的。
We shall deliver the goods after getting the full payment but XX percent deposit is needed.
这是必须要收到全额货款后才放货，但是XX％的定金还是要滴。

You must pay deposit first,we'll deliver goods when we get the payment.

You have to put down down payment first, the style arrives to pay goods