My simple example

Here is a sketch, mix of examples.
Send data and sleep 20 Sec.
I accept suggestions.

#include "LoRaWan_APP.h"
#include "Arduino.h"


#define timetosleep 1000
#define timetowake 20000
static TimerEvent_t sleep;
static TimerEvent_t wakeup;
uint8_t lowpower=1;

/*
 * set LoraWan_RGB to Active,the RGB active in loraWan
 * RGB red means sending;
 * RGB purple means joined done;
 * RGB blue means RxWindow1;
 * RGB yellow means RxWindow2;
 * RGB green means received done;
 */

/*LoraWan Class*/
DeviceClass_t  CLASS=LORAWAN_CLASS;
/*OTAA or ABP*/
bool OVER_THE_AIR_ACTIVATION = LORAWAN_NETMODE;
/*ADR enable*/
bool LORAWAN_ADR_ON = LORAWAN_ADR;
/* set LORAWAN_Net_Reserve ON, the node could save the network info to flash, when node reset not need to join again */
bool KeepNet = LORAWAN_Net_Reserve;
/*LoraWan REGION*/
LoRaMacRegion_t REGION = ACTIVE_REGION;

/* Indicates if the node is sending confirmed or unconfirmed messages */
bool IsTxConfirmed = false;
/*!
* Number of trials to transmit the frame, if the LoRaMAC layer did not
* receive an acknowledgment. The MAC performs a datarate adaptation,
* according to the LoRaWAN Specification V1.0.2, chapter 18.4, according
* to the following table:
*
* Transmission nb | Data Rate
* ----------------|-----------
* 1 (first)       | DR
* 2               | DR
* 3               | max(DR-1,0)
* 4               | max(DR-1,0)
* 5               | max(DR-2,0)
* 6               | max(DR-2,0)
* 7               | max(DR-3,0)
* 8               | max(DR-3,0)
*
* Note, that if NbTrials is set to 1 or 2, the MAC will not decrease
* the datarate, in case the LoRaMAC layer did not receive an acknowledgment
*/
uint8_t ConfirmedNbTrials = 1;

/* Application port */
uint8_t AppPort = 2;

/*the application data transmission duty cycle.  value in [ms].*/
uint32_t APP_TX_DUTYCYCLE = 15000;

/* Prepares the payload of the frame */
static void PrepareTxFrame( uint8_t port )
{
    AppDataSize = 4;//AppDataSize max value is 64
    AppData[0] = 0x00;
    AppData[1] = 0x02;
    AppData[2] = 0x01;
    AppData[3] = 0x03;
}


void setup() {
    BoardInitMcu();
    Serial.begin(115200);
    #if(AT_SUPPORT)
    Enable_AT();
    #endif
    DeviceState = DEVICE_STATE_INIT;
    LoRaWAN.Ifskipjoin();
    Serial.println( "[stup] INIT");
    #if(AT_SUPPORT)
      getDevParam();
    #endif
    Serial.println ("");
    Serial.println("[pram] ***********************************");
    printDevParam();
    Serial.println("[pram] ***********************************");
    Serial.println ("");
    Serial.printf("[stup] LoRaWan Class%X  start! \r\n",CLASS+10);   
    LoRaWAN.Init(CLASS,REGION);
    Serial.println( "[stup] JOIN");
    LoRaWAN.Join();
    delay(1000);   

    TimerInit( &sleep, OnSleep );
    TimerInit( &wakeup, OnWakeup );
    OnSleep();
}

void loop()
{
  if(lowpower)
  {
  //note that LowPower_Handler() run six times the mcu into lowpower mode;
  LowPower_Handler();
  }					
}

void OnSleep()
{
  Serial.printf("[lowp] lowpower mode  %d ms\r\n",timetowake);
  Serial.println("---------------------------zzzzzzzz----------------------------");
  lowpower=1;
  //timetosleep ms later wake up;
  TimerSetValue( &wakeup, timetowake );
  TimerStart( &wakeup );
}
void OnWakeup()
{
  Serial.printf("[wkup] wake up, %d ms later into lowpower mode.\r\n",timetosleep);
  uint32_t currentTime=TimerGetCurrentTime()/1000;
  Serial.printf("[time] upTime: %d sec. \r\n",currentTime);   
  lowpower=0;
  //timetosleep ms later into lowpower mode;
  Serial.print( "[ttn ] ");//sending
  PrepareTxFrame( AppPort );
  LoRaWAN.Send();
  delay(1000); 
      
    /*
      Serial.println( "CYCLE");
      // Schedule next packet transmission
      TxDutyCycleTime = APP_TX_DUTYCYCLE + randr( 0, APP_TX_DUTYCYCLE_RND );
      LoRaWAN.Cycle(TxDutyCycleTime);
    */  
    
  Serial.println("[ttn ] SEND");
  LoRaWAN.Sleep();
  
  TimerSetValue( &sleep, timetosleep );
  TimerStart( &sleep );
}

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