My board works fine when I "stack" it on top of an Arduino Uno (5V logic levels)
However, when I use a low voltage Arduino (MKR Wifi 1010), it doesn't ever pass the initial handshake from modem.begin().
I've wired it up per the wiki such that 5V on the SIM7000A board is wired to a 3.3V voltage source on the Arduino (https://github.com/botletics/SIM7000-LTE-Shield/wiki/Pinouts#external-host-board-wiring).
The call to modem.powerOn works (the board comes to life a couple of seconds later).
However, none of the modem commands seem to succeed. I've tried swapping the TX/RX wires to see if I had a wiring mistake, but no such luck. Here's the output from the console: