Gutenberg custom setting panel not saving meta data

Hi all,

I try to update and save metadata using the PluginDocumentSettingPanel first I registered the custom meta field in PHP. The settings panel is working, but the value won’t save.

Here is my PHP code:

function commpro_register_meta_values(){
    register_meta( 'post', '_custom_header_image', [
        'show_in_rest' => true,
        'single' => true,
        'type' => 'string',
        'auth_callback' => function() {
            return current_user_can( 'edit_posts' );
        }
    ]);
}

function commpro_register_script(){
    wp_enqueue_script(
		'commpro-meta-plugin', 
		plugin_dir_url(__FILE__) . '/build/script.js', 
		[ 'wp-edit-post', 'wp-element', 'wp-components', 'wp-plugins', 'wp-data' ],
		false,
		false
	);
}

add_action('init', 'commpro_register_meta_values');
add_action('enqueue_block_editor_assets', 'commpro_register_script');

And here are the JS files that are compiled into script.js

const { registerPlugin } = wp.plugins;

import CommproCustomSidebarItem from './panel.js';

registerPlugin( 'commpro-custom-sidebar-item', {
    render: CommproCustomSidebarItem,
    icon: '',
} );

const { compose } = wp.compose;
const { withSelect, withDispatch } = wp.data;
const { PanelRow, TextControl } = wp.components;
const { PluginDocumentSettingPanel } = wp.editPost;

const CommproCustomSidebarItem = ( {postMeta, postType, setPostMeta} ) => {
    if (postType !== 'testimonial') return null;

    return(
        <PluginDocumentSettingPanel
            name="custom-header"
            title="Aangepaste header afbeelding"
            className="custom-header"
        >
            <PanelRow>
                <TextControl
                    label="Dit is een aangepast veld"
                    value={ postMeta._custom_header_image }
                    onChange={ ( value ) => setPostMeta( { _custom_header_image: value } )}
                />
            </PanelRow>
        </PluginDocumentSettingPanel>
    )
};

export default compose([
    withSelect( (select) => {  
        return {
            postMeta: select( 'core/editor' ).getEditedPostAttribute( 'meta' ) || {},
            postType: select( 'core/editor' ).getCurrentPostType()
        };
    }),

    withDispatch( ( dispatch ) => {
        return {
            setPostMeta( newMeta ){
                console.log(newMeta);
                dispatch( 'core/editor' ).editPost( { meta: newMeta } );
            }
        }
    })
]) (CommproCustomSidebarItem);