Password protect visibility page error

I have found this code from here

When I add this, its redirecting to /wp-login.php?action=postpass and showing a complete white screen.

Can anyone please see if there’s any problem in the code? and give the correct one so that it works correctly.

I am adding the code below.

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function my_custom_password_form() {
		global $post;
		$label = 'pwbox-' . ( empty( $post->ID ) ? rand() : $post->ID );
		$output = '
		<div class="pa-lck-section">
			<div class="container">
				<form action="' . esc_url( site_url( 'wp-login.php?action=postpass', 'login_post' ) ) . '" class="form-inline post-password-form" method="post">
					<p>' . __( '<b>This is a subscribers only content.</b><br> If you are already subscribed then enter your key you have received via mail and enjoy surfing. Incase you have not subscribed yet, please subscribe to receive your access key.' ) . '</p>
					<label for="' . $label . '">' . __( 'Enter Access Key' ) . ' <input name="post_password" id="' . $label . '" type="password" size="20" class="form-control" /></label><button type="submit" name="Submit" class="button-primary">' . esc_attr_x( 'Submit', 'post password form' ) . '</button>
				</form>
			</div>
		</div>';
	return $output;
}
add_filter('the_password_form', 'my_custom_password_form', 99);