Error: Call to undefined method RWMB_Heading_Field::input_description()

Yup looks like wp-content/plugins/meta-box/inc/fields/heading.php is just missing the function to return the description. Adding the method fixes everything.

I added this function below. Although as I’m looking through the code again it looks like it might be trying to call the input_description function in my theme’s RWMB_Field’s abstract class instead of from the plugin’s.

    /**
     * Display field description.
     *
     * @param array $field Field parameters.
     * @return string
     */
    protected static function input_description( $field ) {
        $id = $field['id'] ? ' id="' . esc_attr( $field['id'] ) . '-description"' : '';
        return $field['desc'] ? "<p{$id} class='description'>{$field['desc']}</p>" : '';
    }