Gutenberg custom meta blocks not saving meta to custom post type

Question

I have a site with a custom post type set up to define home page call to action boxes.

The title, description, and featured image are all handled by the default blocks/features of the edtior, but I'm trying to add a custom block to save a url to the post's meta.

The block renders properly but it is not saving the meta data, the updateBlockValue function is defintely being called.

I have used almost identical code to create custom meta blocks for pages and posts. Does this method just not work with custom post types?

this is the code I'm using:

PHP

function wb_blocks() {

    wp_register_script(
        'wb-blocks-js',
        get_template_directory_uri() . '/scripts/block.js',
        array( 'wp-blocks', 'wp-editor', 'wp-element','wp-components' )
    );
    register_block_type( 'ray/homebox-link-url', array(
        'editor_script' => 'wb-blocks-js',
    ) );

}
add_action( 'init', 'wb_blocks' );
function wb_register_block_meta() {

    register_meta( 'post', 'homebox_link_url', array(
        'show_in_rest' => true,
        'single' => true,
        'type' => 'string',
    ) );

}

add_action( 'init', 'wb_register_block_meta' );

JS

registerBlockType( 'ray/homebox-link-url', {
title: 'Homebox Link',
icon: 'universal-access-alt',
category: 'layout',
attributes: {
    blockValue: {
        type: 'string',
        source: 'meta',
        meta: 'homebox_link_url',
    }
},

edit: function( props ) {
    var setAttributes = props.setAttributes;

    function updateBlockValue( blockValue ) {
        setAttributes({ blockValue });
    }

    return el(
       'div',
       { className: "homebox-link-url" },
        el( 'h5',{}, 'URL to link to:'),
        el (TextControl,
        {
            onChange: updateBlockValue,
            value: props.attributes. blockValue,
        })
    );
},

save: function( props ) {
     return null;
},
} );