how to redirect to login page then redirect back to the previous page in php

Question

I know there are many questions about this, but i could not find an answer for when i want the login to always redirect to the main page except when the user clicks on the "submit" page it should log in then allow the user to add a suggestion. I managed to redirect to log in page after clicking on the "submit" page but after that, it redirects to the main page and i get stuck in a loop. (Index is my main page). (suggest is where i want to force the log in). Here is what i have done so far: at the top of my suggest.php:

<?php
if(!isset($_SESSION['user_id'])) 
{
    $_SESSION["login_redirect"] = $_SERVER["PHP_SELF"];
    header("Location: login2.php");
    exit;
}
?>

Login-form.php:

<?php
if(isset($_POST['loginbutton'])){
require 'dbh.inc.php'; 

$UsernameEmail = $_POST['username/email'];
$password = $_POST['password'];


if (empty($UsernameEmail)||empty($password)){
    header("location: ../Index.php?error=emptyfields&username");
    exit();
}else {
    $sql = "SELECT * FROM users WHERE username=? OR email =? ;" ;
    $stmt = mysqli_stmt_init($conn);

    if(!mysqli_stmt_prepare($stmt,$sql)){
header("location: ../Index.php?error=sqlerror");
    exit();

    }
    else {

    mysqli_stmt_bind_param($stmt , "ss", $UsernameEmail,$UsernameEmail );
    mysqli_stmt_execute($stmt);
   $result = mysqli_stmt_get_result($stmt); 
   if($row = mysqli_fetch_assoc($result)){
       $pwdCheck = password_verify($password , $row['password']);
       if($pwdCheck == false ){
           header("location: ../Index.php?error=wrongPassword");
         exit();  
       }  else if ($pwdCheck == true ){
           session_start();
           $_SESSION['user_id']= $row['id'];
            $_SESSION['user_name']=  $row['username'];

       } else {
              header("location: ../Index.php?error=wrongPassword");
         exit();  
       }

   }
   else { 
       header("location: ../Index.php?nouser/emailmatch");
    exit(); 
   }

    }

}   
}
else {

header("Location: ../Index.php?succses");
    exit();
}

I also tried this code in SUGGEST.php

<?php
if(!isset($_SESSION['user_id'])) 
{
    header('Location: login2.php?redirect=SUGGEST.php');
    exit;
} 
?>

and this one in login-form.php but that didn't work either

if (isset($_GET['redirect'])) {
    header('Location: ' . $_GET['redirect']);
} 

that is my first time coding in php, so i would really apperiate a detailed answer. Thank you

Answer 1

You should use session_start(); at first line of each page, actually without any space or break-line before that!