M66 - problem with communication to the device

I have a problem with sending of the synchronizing AT string, as and the AT commands to the device M66 - it doesn’t answer at all. The voltage level to the device is 2.8V - I’m using level translation from 5V, speed is 19200, one start and one stop bit, no parity, UART interface (pins 17 and 18, RTS connected to ground). But when switch the device off, I receive the status string “NORMAL POWER DOWN”. The sim card is not inserted and the device is not synchronized to the GSM network (status led is around 60ms on and 800ms off).
What could be the problem?

Thanks in advance.

Please change the baud rate to 115200 for testing, and send AT with a space and carriage return at the end