How to extend WordPress REST API to include custom meta fields for a custom post type?

Question

I'm working on a custom WordPress project where I’ve registered a custom post type called parcel. It has several custom meta fields like pickup_pincode, drop_pincode, and delivery_type.

I want to expose these custom fields via the WordPress REST API when fetching the parcel posts (e.g., /wp-json/wp/v2/parcel).

I’ve registered the custom post type using register_post_type, and the meta fields using register_post_meta.

Here’s what I’ve tried in functions.php:

function register_parcel_meta_fields() {
    register_post_meta('parcel', 'pickup_pincode', [
        'show_in_rest' => true,
        'type'         => 'string',
        'single'       => true,
    ]);
}
add_action('init', 'register_parcel_meta_fields');

I registered the meta fields using register_post_meta() with 'show_in_rest' => true, expecting them to appear automatically in the REST API response for my custom post type parcel. However, when I fetch the data via /wp-json/wp/v2/parcel, the custom fields like pickup_pincode are missing. I expected them to be visible in the JSON response but they’re not showing up. I’m unsure if I need to do more or hook into a different filter.

It's strange, your code works on my test site. edit your question to add the code you use to register the custom post type. — mmm
– mmm, Commented Jul 8 at 15:41

Farees Ahmed · Accepted Answer · 2025-07-10 05:41:58Z

If the custom meta fields aren't showing in the REST API response, there are a few key things to check and potentially adjust.

1. Make sure your custom post type is set up correctly for REST

When registering the post type with register_post_type(), make sure you’ve included:

'show_in_rest'=> true,

Example:

register_post_type('parcel', [ 'label' => 'Parcels', 'public' => true, 'show_in_rest' => true, // THIS is important 'supports' => ['title', 'editor', 'custom-fields'], // other args... ]);

2. Ensure Meta Fields Are Registered on `rest_api_init`

Instead of init, use the rest_api_init hook when calling register_post_meta(). This ensures the fields are properly registered when the REST API is initialized:

functionregister_parcel_meta_fields() { register_post_meta('parcel', 'pickup_pincode', [ 'show_in_rest' => true, 'type' => 'string', 'single' => true, ]); register_post_meta('parcel', 'drop_pincode', [ 'show_in_rest' => true, 'type' => 'string', 'single' => true, ]); register_post_meta('parcel', 'delivery_type', [ 'show_in_rest' => true, 'type' => 'string', 'single' => true, ]); } add_action('rest_api_init', 'register_parcel_meta_fields');

3. Check Response Format

When you fetch /wp-json/wp/v2/parcel, scroll to the meta object in the JSON response. The custom fields appear there, like so:

"meta": { "pickup_pincode": "123456", "drop_pincode": "654321", "delivery_type": "express" }

If you don't see the meta key at all:

Ensure you're using register_post_meta() as shown.
Double-check there's actually meta data saved for those fields on the post.
Try adding 'auth_callback' => '__return_true' to the meta registration temporarily for testing:

register_post_meta('parcel', 'pickup_pincode', [ 'show_in_rest' => true, 'type' => 'string', 'single' => true, 'auth_callback' => '__return_true', // for testing ]);

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How to extend WordPress REST API to include custom meta fields for a custom post type?

1 Answer 1

1. Make sure your custom post type is set up correctly for REST

2. Ensure Meta Fields Are Registered on `rest_api_init`

3. Check Response Format

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Collectives™ on Stack Overflow

1 Answer 1

1. Make sure your custom post type is set up correctly for REST

2. Ensure Meta Fields Are Registered on rest_api_init

3. Check Response Format

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2. Ensure Meta Fields Are Registered on `rest_api_init`