POST ( $url, [$body_content, %$headers] )

##</code><code>##

my $client = REST::Client->new();
$client->setHost($wiki);
... # got token

# preparing a request:
$request = "action=edit&title=LookupAutomationTest&summary=test%20summary&text=article%20content";
$request .= '&format=json';
$request .= "&token=$token";
$client->POST($api, $request); # << separate path (e.g. "/mediawiki/api.php") from the request-params e.g. the ? part which is now in string $request.