Invalid conversion from 'const char*' to 'const uint8_t*

[BouTayehGaby]

Hello,

I am trying to use the LMIC library for my ESP32 Heltec. I am getting the following errors:

Arduino: 1.8.9 (Windows 10), Board: "Heltec WiFi LoRa 32, Disabled, Default, 240MHz (WiFi/BT), QIO, 40MHz, 4MB (32Mb), 921600, None"

C:\..\..\Documents\libraries\arduino-lmic-master\src\hal\hal.cpp: In function 'ssize_t uart_putchar(void*, const char*, size_t)':
C:\..\..\Documents\libraries\arduino-lmic-master\src\hal\hal.cpp:234:41: 

error: invalid conversion from 'const char*' to 'const uint8_t* {aka const unsigned char*}' [-fpermissive] 
return LMIC_PRINTF_TO.write(buf, len);

     ^

In file included from C:\..\..\AppData\Local\Arduino15\packages\esp32\hardware\esp32\1.0.2\cores\esp32/Arduino.h:160:0,
from C:\..\..\Documents\libraries\arduino-lmic-master\src\hal\hal.cpp:11:
C:\..\..\AppData\Local\Arduino15\packages\esp32\hardware\esp32\1.0.2\cores\esp32/HardwareSerial.h:67:12: note:   

initializing argument 1 of 'virtual size_t HardwareSerial::write(const uint8_t*, size_t)
size_t write(const uint8_t *buffer, size_t size);**

    ^

exit status 1
Error compiling for board Heltec WiFi LoRa 32.

Any idea why?