#include <ESP8266WiFi.h>
#define PubNub_BASE_CLIENT WiFiClient
#define PUBNUB_DEFINE_STRSPN_AND_STRNCASECMP

#include <PubNub.h>

String pubkey = "pub-c-4a9cdbca-5688-4939-a852-f63cf6743980";
String subkey = "sub-c-9b4067ae-1293-11e9-b4a6-026d6924b094";
String pubchannel = "sec-c-NmFiYjliODYtMTc3Mi00YTMzLTg0OWMtMDgzYjE2ZGUwNzg5";

void setup() {
    /* For debugging, set to speed of your choice */
    Serial.begin(9600);


    /* Start the Pubnub library by giving it a publish and subscribe
       keys */
    PubNub.begin(pubkey, subkey);
}

void loop() {
    /* Maintain DHCP lease. For other HW, you may need to do
       something else here, or maybe nothing at all. */


    /* Publish message. You could use `auto` here... */
    PubNonSubClient *pclient = PubNub.publish(pubchannel, ""message"");
    if (!pclient) return;
    PublishCracker cheez;
    cheez.read_and_parse(pclient);
    /** You're mostly interested in `outcome()`, and,
        if it's "failed", then `description()`.
    */
    Serial.print("Outcome: "); Serial.print(cheez.outcome());
    Serial.print(' '); Serial.println(cheez.to_str(cheez.outcome()));
    Serial.print("description: "); Serial.println(cheez.description());
    Serial.print("timestamp: "); Serial.println(cheez.timestamp());
    Serial.print("state: "); Serial.print(cheez.state());
    Serial.print(' '); Serial.println(cheez.to_str(cheez.state()));
    pclient->stop();

    /* Wait for news. */
    PubSubClient *sclient = PubNub.subscribe(subchannel);
    if (!sclient) return; // error
    String msg;
    SubscribeCracker ritz(sclient);
    while (!ritz.finished()) {
        ritz.get(msg);
        if (msg.length() > 0) {
            Serial.print("Received: "); Serial.println(msg);
        }
    }
    sclient->stop();

    delay(1000);
}

Error:-
node_mcu_test_code:44:46: error: 'subchannel' was not declared in this scope

     PubSubClient *sclient = PubNub.subscribe(subchannel);

                                              ^

node_mcu_test_code:54:14: error: 'class PubSubClient' has no member named 'stop'

     sclient->stop();

              ^

exit status 1
no matching function for call to 'PubNub::begin(String&, String&)'