PHP POST does not redirect properly - php

Question

I have two different sites and want to pass data via a form from the first to the second page.
The form looks as follows (simplified):
<form method="POST" action="https://othersite.me/login.php">
<label class="title">
E-Mail
</label>
<input name="luser" type="email">
<label class="title">
Password
</label>
<input name="lpasswd" type="password">
<input type="submit" value="Login">
</form>
The php code othersite.me/login.php looks as follows:
<?php
$email=Format::input($_POST['luser']?:$_GET['e']);
$passwd=Format::input($_POST['lpasswd']?:$_GET['t']);
?>
<form method="POST" action="login.php">
<label class="title">
E-Mail
</label>
<input name="luser" type="email" value="<?php echo $email; ?>">
<label class="title">
Password
</label>
<input type="password" value="<?php echo $passwd; ?>">
<input type="submit" value="Submit">
</form>
Now I expect that when I enter some data on the first page, the data is transferred to otherpage.me/login.php and displayed in the appropriate fields.
Curiously, after pressing the submit button, the website is redirected to othersite.me/login.php for less than a second and then automatically to othersite.me/index.php.
If I use GET instead of POST, the form works as expected and stays on othersite.me/login.php.
How is this possible and how can I fix that. Do you have some ideas?

Answer 1

Why do you need two php file to do this? You can use action="<?php echo $_SERVER['PHP_SELF']; ?>" in your login.php and start processing the submitted data there. You can follow this instruction

Answer 2

I don't have reputation to comment yet so I will answer.
In the othersite.me/login.php if you have permission paste the code below
ini_set('display_errors', 1); ini_set('display_startup_errors', 1); error_reporting(E_ALL);
This will return all warnings and fatal errors