ESP32 UART1 problem

[WiFive]

That's fine but remember you don't have to use default pins for uart you can reconfigure to any pin using gpio matrix.

[MaiNhan]

Bacause Pin 9 and 10 (U1Rx and U1Tx) were used for flash chip. To use UART1 in ESP32, You can remap Rx and Tx by using bellow instruction:
Serial1.begin(9600, SERIAL_8N1, 4, 2);
I hope it a little bit help you.!!!