Hi @uandiweb,
If you would like to add code to the end of the <body> section, you can replace that line with this:
add_action( 'wp_head', function () { ?>
That adds to the head section. New templates should support wp_body_open. That is primarily for JavaScript but can use also for other purposes. Old templates don’t support this.
Ah, my mistake. If you want to add code to the end of the <body> section, right before the </body> tag, you should actually replace it with this line:
add_action( 'wp_footer', function () { ?>
As @tapiohuuhaa said, if you have a theme which supports it, you can alternatively add code to the start of the <body> section, right after the <body> tag, you can use this as the first line:
add_action( 'wp_body_open', function () { ?>
