WordPress REST API create custom post type not working

Question

I am trying to create a custom post using WordPress REST API. The problem is that I can create the custom post when logged in as an administrator. But when I try to create the post while logged in as a custom role 'new_role', the API is giving the below error response.

{
    "code": "rest_cannot_update",
    "message": "Sorry, you are not allowed to edit the letter_intro custom field.",
    "data": {
        "key": "letter_intro",
        "status": 403
    }
}

And the post get created without having the post_meta values. I tried adding the capability by adding the below code in function.php

add_action('rest_api_init', function () {
$new_role = get_role('new_role');
$new_role->add_cap('edit_post', true);
$new_role->add_cap('edit_post_meta', true);
...
...

But it is not working.

Answer 1

I was able to resolve it by using the below code.

$args = array(
            'labels' => $labels,
            'description' => 'Custom post',
            'public' => true,
            'menu_position' => 5,
            'supports' => array('title', 'editor', 'thumbnail', 'author', 'excerpt', 'comments', 'custom-fields'),
            'has_archive' => true,
            'show_in_rest' => true,
            'rest_base'    => 'letters',
            'capabilities' => array(
        'edit_post' => 'edit_letter',
        'edit_posts' => 'edit_letters',
        'publish_posts' => 'publish_letters',
        'read_post' => 'read_letter',
        'delete_post' => 'delete_letter'
    ),
        );
        register_post_type('letter', $args);

Then add those capabilities to the required roles.

function new_caps()
{
     $new_role = get_role('new_role');
     $new_role->add_cap('edit_letter', true);
     $new_role->add_cap('edit_letters', true);
     $new_role->add_cap('publish_letters', true);
     $new_role->add_cap('read_letter', true);
     $new_role->add_cap('delete_letter', true);

     $admins = get_role( 'administrator' );
     $admins->add_cap('edit_letter', true);
     $admins->add_cap('edit_letters', true);
     $admins->add_cap('publish_letters', true);
     $admins->add_cap('read_letter', true);
     $admins->add_cap('delete_letter', true);
}


add_action('init', 'new_caps', 11);