网页版支付宝 missing-method（缺少方法名参数）

<form id='alipaysubmit' name='alipaysubmit' action='http://openapi.alipay.com/gateway.do?charset=UTF-8' method='POST'>
<input type='hidden' name='method' value='alipay.trade.page.pay'/>
<input type='hidden' name='app_id' value='2021001159663736'/>
<input type='hidden' name='timestamp' value='2020-08-26 15:51:30'/>
<input type='hidden' name='format' value='json'/>
<input type='hidden' name='version' value='1.0'/>
<input type='hidden' name='alipay_sdk' value='alipay-easysdk-php-2.0.0'/>
<input type='hidden' name='charset' value='UTF-8'/>
<input type='hidden' name='sign_type' value='RSA2'/>
<input type='hidden' name='biz_content' value='{"subject":"商品名称1","out_trade_no":"2020082627910638047310","total_amount":"0.20","product_code":"FAST_INSTANT_TRADE_PAY"}'/>
<input type='hidden' name='sign' value='ZU1E6Uc9sf8PCO5LdBrfkAdXiiK2WCQGX1BtVnjXHMve3MghpLrBiFik6X7taw0cnygZvSkka+y62Z3RY9Toog0NFBLQZPvfVsSu/5rSkrFb09oDmeDrxFG+PqNm4kje5tQTikF831yzKaPbJZciYOaMa9yqpDEXbML025UJ2+dqT7r4LPDKcQ5bOe4lW7YSRdbUvOcaZ4gSEZ9duV0ueyF/ibOCXpsShJY5llPEY3LEYSR8WO0JliOT5yxzoE65bj57UsRXSItrTSKjYncs/fSzDFUMwGbCsOnBiSzveiDwnA4ai8WzVkwKOM5VNQ0fRk/lniwAfiAtVNlrVMpqKA=='/>
<input type='submit' value='ok' style='display:none;''>
</form>
<script>document.forms['alipaysubmit'].submit();</script>

有method，为什么还报错