BPI-Leaf-S3 - Serial1 no connect

I have a problem with Serial1, I am trying to get it working on 18(RX1) and 17(TX1) and unfortunately I am not able to get it working. Can you advise me what to do with it? #include <HardwareSerial.h> HardwareSerial SerialPort(1); // use UART1 SerialPort.begin(115200, SERIAL_8N1, 18, 17);