Serial creat session error when use serial mode

[dongdong-cyber]

I have a development integrated circuit board for a smart hardware device, which includes an SOC side and an MCU side. The SOC and MCU are connected via a serial port. I use commands on the SOC, and the MCU runs an RT-Thread system. When I execute echo "Hello MCU" > /dev/ttyTHS1, I can see the printed message on the serial port. However, when using the serial port, the agent fails to register a session. How can I resolve this issue?

Agent side

uartside

mcuside

[dongdong-cyber]

mcuside