Can anybody help?

Here's the code

--- cut ---
#include <M5Stack.h>
#include "LoRaWan.h"

//LoRa
char buffer[256];
long sentMillis = 0;
long currentMillis = 0;
long interval = 15000;
//byte payload[2];

void setup() {
/* Prepare M5STACK */
M5.begin();

initlora();

M5.Lcd.println("Started");
}

void loop() {

currentMillis = millis();
if (currentMillis - sentMillis > interval) {
sendobject();
}

M5.update();
}

void initlora() {

lora.init();

delay(1000);

memset(buffer, 0, 256);
lora.getVersion(buffer, 256, 1);
Serial.print(buffer);

memset(buffer, 0, 256);
lora.getId(buffer, 256, 1);
Serial.print(buffer);

lora.setId(NULL, "aaa", "bbb");
lora.setKey(NULL, NULL, "ccc");

M5.Lcd.println("setDeviceMode");
lora.setDeviceMode(LWOTAA);
M5.Lcd.println("setDataRate");
lora.setDataRate(DR5, EU868);

lora.setChannel(0, 868.1);
lora.setChannel(1, 868.3);
lora.setChannel(2, 868.5);
lora.setChannel(3, 867.1);
lora.setChannel(4, 867.3);
lora.setChannel(5, 867.5);
lora.setChannel(6, 867.7);
lora.setChannel(7, 867.9);

lora.setReceiveWindowFirst(0, 868.1);
lora.setReceiveWindowSecond(869.525, DR3);

lora.setPower(14);
lora.setPort(1);
lora.setAdaptiveDataRate(true);
//lora.setDutyCycle(false);
//lora.setJoinDutyCycle(false);
while (!lora.setOTAAJoin(JOIN, 10));
}

void sendobject() {
bool result = false;

sentMillis = millis();

M5.Lcd.println("Sending");

result = lora.transferPacket("Hello World!", 5);
//result = lora.transferPacket(payload, sizeof(payload), 5);

if (result == true) {
M5.Lcd.println("Sent");

} else {
M5.Lcd.println("Error");
}
}