PHP - 提交日期/时间/通过$ _POST从foreach循环中选择输入值不返回任何内容

I'm having an issue in submitting input values in a form from a page to another, with the post method; when I try getting the values with $_POST['input_name'], it doesn't return anything, and I get a "Undefined index" notice on the page I'm sending the data to. The only value that is passed correclty is ['studentid']. the form is inside of a foreach loop. I'm pretty new to php, so I might be ignoring something really basic.I'm having an issue in submitting input values