Unable to Join through OTAA , It worked only for one time

#include <lmic.h>
#include <hal/hal.h>
#include <SPI.h>

// This EUI must be in little-endian format, so least-significant-byte
// first. When copying an EUI from ttnctl output, this means to reverse
// the bytes. For TTN issued EUIs the last bytes should be 0xD5, 0xB3,
// 0x70.
static const u1_t PROGMEM APPEUI[8]={ 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00 };
void os_getArtEui (u1_t* buf) { memcpy_P(buf, APPEUI, 8);}

// This should also be in little endian format, see above.
static const u1_t PROGMEM DEVEUI[8]={ 0x9B, 0xB1, 0x04, 0xD0, 0x7E, 0xD5, 0xB3, 0x70 };
void os_getDevEui (u1_t* buf) { memcpy_P(buf, DEVEUI, 8);}

// This key should be in big endian format (or, since it is not really a
// number but a block of memory, endianness does not really apply). In
// practice, a key taken from ttnctl can be copied as-is.
// The key shown here is the semtech default key.
static const u1_t PROGMEM APPKEY[16] = { 0x6B, 0xEC, 0xF4, 0xD8, 0x6C, 0x84, 0x78, 0x7A, 0xE3, 0xB2, 0x36, 0xC5, 0x1C, 0x37, 0x6F, 0x55 };
void os_getDevKey (u1_t* buf) { memcpy_P(buf, APPKEY, 16);}

static uint8_t mydata = “Hello 3A!”;
static osjob_t sendjob;

// Schedule TX every this many seconds (might become longer due to duty
// cycle limitations).
const unsigned TX_INTERVAL = 30;

// Pin mapping
const lmic_pinmap lmic_pins = {
.nss = 10,
.rxtx = LMIC_UNUSED_PIN,
.rst = 9,
.dio = {2, 6, 7},
};

void onEvent (ev_t ev) {
Serial.print(os_getTime());
Serial.print(": ");
switch(ev) {
case EV_SCAN_TIMEOUT:
Serial.println(F(“EV_SCAN_TIMEOUT”));
break;
case EV_BEACON_FOUND:
Serial.println(F(“EV_BEACON_FOUND”));
break;
case EV_BEACON_MISSED:
Serial.println(F(“EV_BEACON_MISSED”));
break;
case EV_BEACON_TRACKED:
Serial.println(F(“EV_BEACON_TRACKED”));
break;
case EV_JOINING:
Serial.println(F(“EV_JOINING”));
break;
case EV_JOINED:
Serial.println(F(“EV_JOINED”));

        // Disable link check validation (automatically enabled
        // during join, but not supported by TTN at this time).
        LMIC_setLinkCheckMode(0);
        break;
    case EV_RFU1:
        Serial.println(F("EV_RFU1"));
        break;
    case EV_JOIN_FAILED:
        Serial.println(F("EV_JOIN_FAILED"));
        break;
    case EV_REJOIN_FAILED:
        Serial.println(F("EV_REJOIN_FAILED"));
        break;
        break;
    case EV_TXCOMPLETE:
        Serial.println(F("EV_TXCOMPLETE (includes waiting for RX windows)"));
        if (LMIC.txrxFlags & TXRX_ACK)
          Serial.println(F("Received ack"));
        if (LMIC.dataLen) {
          Serial.println(F("Received "));
          Serial.println(LMIC.dataLen);
          Serial.println(F(" bytes of payload"));
        }
        // Schedule next transmission
        os_setTimedCallback(&sendjob, os_getTime()+sec2osticks(TX_INTERVAL), do_send);
        break;
    case EV_LOST_TSYNC:
        Serial.println(F("EV_LOST_TSYNC"));
        break;
    case EV_RESET:
        Serial.println(F("EV_RESET"));
        break;
    case EV_RXCOMPLETE:
        // data received in ping slot
        Serial.println(F("EV_RXCOMPLETE"));
        break;
    case EV_LINK_DEAD:
        Serial.println(F("EV_LINK_DEAD"));
        break;
    case EV_LINK_ALIVE:
        Serial.println(F("EV_LINK_ALIVE"));
        break;
     default:
        Serial.println(F("Unknown event"));
        break;
}

}

void do_send(osjob_t* j){
// Check if there is not a current TX/RX job running
if (LMIC.opmode & OP_TXRXPEND) {
Serial.println(F(“OP_TXRXPEND, not sending”));
} else {
// Prepare upstream data transmission at the next possible time.
LMIC_setTxData2(1, mydata, sizeof(mydata)-1, 0);
Serial.println(F(“Packet queued”));
}
// Next TX is scheduled after TX_COMPLETE event.
}

void setup() {
Serial.begin(115200);
Serial.println(F(“Starting”));

#ifdef VCC_ENABLE
// For Pinoccio Scout boards
pinMode(VCC_ENABLE, OUTPUT);
digitalWrite(VCC_ENABLE, HIGH);
delay(1000);
#endif

// LMIC init
os_init();
// Reset the MAC state. Session and pending data transfers will be discarded.
LMIC_reset();

// Start job (sending automatically starts OTAA too)
do_send(&sendjob);

}

void loop() {
os_runloop_once();
}
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