I am trying to create a WP plugin that calls an external API using HTTP POST. I am using wp_remote_post and my arguments look like this:

$body = array(
    'CustomerID' => '10',
    'Items' => ['5', '7'],
);

What I want to end up with is this as my POST data:

CustomerID=10&Items=5&Items=7

But this does not seems to work as expected... Can anyone point me to the right direction?

Also, how can I log the final request parameters, in the same form the external API will get them?