提交参数时不止哪里多了一个string`<div class="row loan-padding loan-coupon">
<select class="form-control fcs-select border-white" name="placementId" ng-model="invest.coupon" ng-options="coupon.id as coupon.label for coupon in invest.coupons">
<option>使用奖券</option>
</select>
</div>`
最后改成这种写法就对了