How to send the body in wp_remote_post as “raw”?

I got this one working, you have to pass the json_encoded array on the body parameter of the request.

 $customer_details = [
            'first_name' => $first_name,
            'last_name' => $last_name,
            'email' => $email,
        ];

        $customer_details['body'] = json_encode($customer_details);

        $customer = $api->createUpdateCustomer($customer_details);

public function createUpdateCustomer($customer_details) {
        $response = $this->apiCall( "2.0/customers", 'POST', $customer_details);
        $result = json_decode($response);
        return $result;
    }

public function apiCall($baseUrl = null, $method = 'GET', $args = array()) {
        if ( !is_null( $baseUrl ) ) {
            $url = $this->baseUrl . $baseUrl;
        }
        else {
            $url = $this->baseUrl;
        }

        // Populate the args for use in the wp_remote_request call
        $wp_args = array_merge($args, $this->args);
        $wp_args['method']  = $method;
        $wp_args['timeout'] = 30;        

        // Make the call and store the response in $res
        $res = wp_remote_request( $url, $wp_args );        

        // Check for success
        if ( ! is_wp_error( $res ) && ( 200 == $res['response']['code'] || 201 == $res['response']['code'] ) ) {
            return $res['body'];
        } else {
            throw new Exception( "API call didn't go well :(. Either VendHQ Connect Settings are incorrect or VendHQ server is not responding as expected." );
        }
    }