uni.requestPayment错误{"resultCode":"4000","memo":"请开启 API 代理","errMsg":"requestPayment:fail 999"}

uni.requestPayment拉起支付宝支付时，提示错误{"resultCode":"4000","memo":"请开启 API 代理","errMsg":"requestPayment:fail 999"}，是什么意思呢？

uni.requestPayment({
provider: 'alipay',
orderInfo: orderinfo, // 后端返回的付款参数
success: function (res) {
console.log('success:' + JSON.stringify(res));
uni.showLoading({
title: '正在查询支付结果'
});
that.checkPayOff(param.orderNo);
},
fail: function (err) {
console.log('fail:' + JSON.stringify(err));
}
})