Need some help with the A7670e.

[u/biggestguyalive]

Hi all. I'm trying to connect an A7670E 4G modem board to an Arduino Uno R4 WiFi (5 V logic) over UART. The seller provides no documentation, and I couldn't find a datasheet or schematic for this exact board.

What I measured (5 V on VCC, nothing else connected, antenna and SIM fitted):
Power LED steady, D1 blinking, so the module appears to be running
RXD: 1.8–1.9 V, steady
TXD: 1.2 V, steady (I expected about 1.8 V idle)
VDD: about 0 V (a few mV)

My questions:
Does anyone know this board or have a schematic for it?
What logic level do the TXD/RXD pins actually expect: 1.8 V, 3.3 V, or does the board shift to something else?
What is the VDD pin for, and why would it be pulled to ground while powered?
Do EN or PWR_EN need to be driven (high or low) for the modem or its UART to work properly?
Is 1.2 V idle on TXD normal for this kind of board?

I have a BSS138 4-channel level shifter available. I want to confirm the correct logic level before connecting anything to the Arduino. Thanks!