Hi Samuel Mok o/ Thanks for asking...I am afraid I am not knowing exactly what is happen on your code...I have some links to you that might help: It's a problem about callback api (cb). look this links: https://docs.espressif.com/projects/esp-idf/en/latest/esp32/api-reference/peripherals/ledc.html#_CPPv415ledc_cb_param_t or this one: http://webserver2.tecgraf.puc-rio.br/iup/en/ledc.html This marker, _t, is a type of library type definition that are not recognize but your compiler... That is all my efford for now...good luck o/