You’re passing request params incorrectly.
Take a look at Codex page. You can find such example in there:
$response = wp_remote_post( $url, array( 'method' => 'POST', 'timeout' => 45, 'redirection' => 5, 'httpversion' => '1.0', 'blocking' => true, 'headers' => array(), 'body' => array( 'username' => 'bob', 'password' => '1234xyz' ), 'cookies' => array() ) );
So in your case it should look something like this:
$args = array(
'method' => 'POST',
'headers' => array(
'Content-type: application/x-www-form-urlencoded'
),
'sslverify' => false,
'body' => array(
'api' => get_option('API_key'),
'gw' => '1'
)
);
$api_response = wp_remote_post('https://myurl.com/api', $args);