send sms with sim800l and micropyhton

Question

I wrote a program using the ESP32 board, sim800l and micropython to send a message to my phone, but it doesn't work, maybe there is a problem with my code and also the flashing light blinks once every second it means it doesnt connect to network, can anyone help me?

import machine
import time
uart = machine.UART(2, baudrate=9600, tx=17, rx=16)
def send_sms(number, message): 
   uart.write('AT+CMGF=1\r\n')
   time.sleep(1)

   uart.write('AT+CMGS="{}"\r\n'.format(number))
   time.sleep(1)

   uart.write('{}\r\n'.format(message))
   time.sleep(1)

   uart.write('\x1A')
   time.sleep(1)

number = '+1234567890'
message = 'Hello, this is a test message!'
send_sms(number, message)