无法将数据发送到数据库，也不显示任何错误

Question

我正在尝试将数据发送到我的数据库，但没有发送任何内容。也没有显示任何连接错误。 PHP代码中也没有任何错误。 我为db dbh.inc.php创建了两个文件，一个公共连接文件 我在主要的php文件中调用过。

数据库连接：

   <?php
   $dbServername = "localhost";
   $dbUsername = "root";
   $dbPassword = "admin";
   $dbName = "musicianshub";
   $conn = mysqli_connect ($dbServername, $dbUsername, $dbPassword,$dbName);

PHP代码：

<?php


if (isset($_POST['submit'])) {
include 'dbh.inc.php';



      $first = mysqli_real_escape_string($conn, $_POST['first']);
      $last = mysqli_real_escape_string($conn, $_POST['last']);
      $email = mysqli_real_escape_string($conn, $_POST['email']);
      $phone = mysqli_real_escape_string($conn, $_POST['phone']);
      $pwd = mysqli_real_escape_string($conn, $_POST['pwd']);


      if (empty($first) || empty($last) || empty($email) || empty($phone) || 
      empty($pwd)) {
        header("Location: ../signup.php?signup=empty");
        exit();
      }

      else {
        if (!preg_match("/^[a-zA-Z]*$/", $fist) || !preg_match("/^[a-zA-
        Z]*$/", $last)) {
            header("Location: ../signup.php?signup=invalid");
            exit();
        }
        else {
              if (!filter_var($email, FILTER_VALIDATE_EMAIL)) {
                header("Location: ../signup.php?signup=email");
                exit();
          }
          else {
                $sql = "SELECT * FROM users WHERE user_phone='$user_phone'";
                $result = mysqli_query($conn, $sql);
                $resultCheck = mysqli_num_rows($result);

                if ($resultCheck > 0) {
                  header("Location: ../signup.php?signup=phonetaken");
                  exit();
                }
                else {
                  $hashedPwd = password_hash($pwd, PASSWORD_DEFAULT);

                  $sql = "INSERT INTO users (user_first, user_last, 
                  user_email, user_phone, user_pwd) VALUES ('$first', 
                  '$last', '$email', '$phone', '$hashedPwd');";

                  mysqli_query($conn, $sql);


                  header("Location: ../signup.php?signup=success");
                  exit();
                }

          }
          }
          }

         }
         else {
         header("Location: ../signup.php");
          exit();
          }

任何人都可以对它有所了解。 谢谢。