MQ-R no output on uart

Hello, I’m trying to test MQ-R image fetched from here: Mango Pi official website | Tiny and Elegant SBC | mqr for MQ-R board. I flashed image using PhoenixTool which went fine. I’ve connected RX, TX (PB6, PB7) to USB-<serial adapter and GND also but when board is powered (I see green LED is ON) I don’t get any output on serial port. Any idea what I’m doing wrong? Thanks.

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