form POST to same page, request method remains GET

I think you need to remove the trailing slash on this line:

PHP Code:

<form action="/klanten/<?= esc($klant['slug']) ?>/" method="post"> 


Like this:

PHP Code:

<form action="/klanten/<?= esc($klant['slug']) ?>" method="post"> 


Because CI uses regex to match the routes and I think you won't get a match with a trailing slash.

The user guide gives this example:

PHP Code:

$routes->add('product/(:segment)', 'Catalog::productLookup/$1'); 


will only match product/123 and generate 404 errors for other example.

CodeIgniter 4 tutorials (EN/FR) - https://includebeer.com
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