Error with Stm32f103c8t6 (Bluepill)

[Armagedon13]

im using the example multi modbus server

Arduino\libraries\MultiModbus\src\libmodbus\modbus-rtu.cpp:1322:5: error: invalid conversion from 'ssize_t (*)(modbus_t*, uint8_t*, int)' {aka 'int (*)(_modbus*, unsigned char*, int)'} to 'ssize_t (*)(modbus_t*, const uint8_t*, int)' {aka 'int (*)(_modbus*, const unsigned char*, int)'} [-fpermissive]
 1322 |     _modbus_rtu_send,
      |     ^~~~~~~~~~~~~~~~
      |     |
      |     ssize_t (*)(modbus_t*, uint8_t*, int) {aka int (*)(_modbus*, unsigned char*, int)}

the stm32 have 3 hardware serial, and i can't find a library that have 1 serial for master and another separated serial line to slave