tag is ignored when using xml-rpc

When you add content to the post_content, WordPress wraps its own tags around everything and removes certain tags (such as script tags).

Plugins, such as Visual composer let you add raw JS, ie. your script tags.

However, if you don’t want to use a plugin, you can add it directly into your page.php or footer.php (if you want the script for all pages, above closing tag).

For example, if you want this for only your home page, you could create a home.php by duplicating your page.php and renaming it home.php (https://developer.wordpress.org/themes/basics/template-hierarchy/)

Or, if you have a page other than home, you could always duplicate page.php and rename it page-yourpagename.php and insert it there.