plugins – I do not get className in a ServerSideRender component

I'm trying to render a block of PHP with ServerSideRender as follows:

js file:

/ **
* WordPress dependencies
* /
const {__} = wp.i18n;
const {registerBlockType} = wp.blocks;
const {ServerSideRender} = wp.components;

/ **
* Internal dependencies
* /
to import icons from & # 39; ./../../ utils / icons & # 39 ;;

registerBlockType ('name / name of the block', {
title: __ ('block name'),
description: __ (Lorem Ipsum is simply a dummy text of the industry of printing and composition in characters.),
keywords: [ __( 'recent post' ) ],
icon: icons.block,
category: & xyz & # 39;

edit: (props) => {
const {
course name,
attributes,
} = props;

return (
      
    )
}

save: () => {
return null;
}
});

php file:





register_block_type (& # 39; ... / blockname & # 39 ;, array (
& # 39; attributes & # 39; => table (
& # 39; className & # 39; => array (
& # 39; like & # 39; => & # 39; chain & # 39 ;,
)
)
& # 39; render_callback & # 39; => & # 39; render_block & # 39;
));

function render_block ($ attr, $ content) {
return 'txt';
}

Return:

   
SMS

Expected:

   
SMS

Everything seems to work fine but the div with the name of the class is not rendered.

Any suggestion to solve this problem? Thank you in advance.