Url Friendly - redirect 301 or 200

Hi E's,
In this question I get a solution for have friendly URL's in my project: https://www.experts-exchange.com/questions/28484783/Mod-rewrite-Information-from-data-base.html.
What this solution does is check the URL, and if the URL does not exist redirects to router.php. Router.php analyze the URL, and if the friendly URL exists, redirect to the current page. Example: Friendly URL = domain.com/friendly-url correspond to domain.com/friendly_url-php?bla=bli, if I write domain.com/friendly-url router.php send to the page  domain.com/friendly_url-php?bla=bli.
This photo shows how the system works:The system work perfect, the problem is Google assumes a 302 Redirect, when the correct is 301 (the page has been moved permanently) or maybe 200 (the server successfully returned the page).

I thing the problem is the code of .htaccess, don't inform the type of redirect:

RewriteEngine On
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^.*$ router.php [L]

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I try change the last line to:

RewriteRule ^.*$ router.php  [R=301,L]

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But not work

Router.php have this code

<?php
//I will check url and redirect page based and that url
header( "Location: article.php?id=878" ) ; 
?> 

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What changes I have to do for the redirect be 301 or 200?

The best regards, JC