Here’s a fix:
/**
* Add the "Blocks CSS: CSS Editor for Gutenberg Blocks" plugin attributes to the Flex Posts attributes so the WordPress
* REST API schema validates.
*
* @hooked flex_posts_attributes
* @see https://www.ads-software.com/plugins/blocks-css/
* @see flex_posts_register_block() block.php:31
* @see register_block_type()
*
* @param array $attributes The validation schema as registered with register_block_type().
* @return array $attributes
*/
add_filter( 'flex_posts_attributes', function( $attributes ) {
include_once ABSPATH . 'wp-admin/includes/plugin.php';
if( is_plugin_active( 'blocks-css/blocks-css.php' ) ) {
$attributes['hasCustomCSS'] = array(
'type' => 'boolean',
'default' => false,
);
$attributes['customCSS'] = array(
'type' => 'string',
'default' => '',
);
}
return $attributes;
});
…and I’ve created a PR to fix it for all plugins:
https://github.com/Codeinwp/blocks-css/pull/5