Which TXD/RXD (0,1,2, etc) to wire from ESP32-POE to Mitsubishi heat pump?

[dwrowland]

My 1st post on Github, originally in General, maybe it's better here in Q&A?

I can't figure out from the code which TXD/RXD (0,1,2,etc.) the program will try to communicate with the Mitsubishi, I find in the code:

#if SOC_UART_NUM > 2 // SPC_UART_NUM evaluates to '3' for my build
#ifndef RX2
#if CONFIG_IDF_TARGET_ESP32
#define RX2 (gpio_num_t)16

#ifndef TX2
#if CONFIG_IDF_TARGET_ESP32
#define TX2 (gpio_num_t)17

...but GPIO17 is NC on the ESP32-POE board.

I assume it can't be TX0/RX0 because on this board the USB-UART chip uses these.
Does anybody know how to find what the code expects to use?