Wordpress REST Api: add_action( 'rest_api_init', callback) does not call the callback

Question

Problem:

I'm trying to register a custom endpoint for a Wordpress plugin. The problem I face is that when I call the add_action('rest_api_init', callback), the callback function is not being called. In that callback function lives the "register_rest_route()" method, which in it's turn is not being called and I am unable to register any custom endpoints.

• I'm using docker for development
• No errors are being thrown

Code:

public function register()
    {
        $this->setup_init();

    }
    
    public function setup_init()
    {
        var_dump('print1');

        add_action('rest_api_init', array($this, 'register_custom_endpoints'));
    }
    
    public function register_custom_endpoints()
    {

        var_dump('print2');
        die();

        register_rest_route('test', '/test', array(
            'methods'  => 'GET',
            'callback' => 'menu_setup',
        ));
    }

Question:

The code reaches the "var_dump('print1')", but the the "var_dump('print2')" is never reached. Am I missing something here?

Answer 1

After trying many options I found out that changing: "Setting -> permalinks -> common settings" to anything else then the option "Plain" solved the issue. The callback method is now being reached, and my custom endpoints are being registered.

Answer 2

Reading your question and self-answer, you are using "Plain permalinks".

You wonder why it doesn't work.

Here's the answer, from the official WordPress documentation.

Basically, when you use plain permalinks you revert to a classic website with a lot of URL parameters. When using REST, your calls will need to be translated into that system in order for them to work.

Here's a simple example:

Imagine you want to get the blog post with id = 123.

With pretty permalinks, you'd call:

https://example.com/wp-json/wp/v2/posts/123

With plain permalinks, you have to call:

https://example.com/?rest_route=/wp/v2/posts/123