in esp32-hal-timer.h
timerBegin function is:
hw_timer_t * timerBegin(uint8_t timer, uint16_t divider, bool countUp);
but at the document:
timerBegin
This function is used to configure the timer. After successful setup the timer will automatically start.
hw_timer_t * timerBegin(uint32_t frequency);
frequency
select timer frequency in Hz. Sets how quickly the timer counter is “ticking”.
This function will return timer
structure if configuration is successful. If NULL
is returned, error occurs and the timer was not configured.