vesc <-> arduino micro troubleshooting UART issues

Hello,

I'm trying to get the simple UART example from SolidGeek arduino UART lib to work (on an arduino micro)

https://github.com/SolidGeek/VescUart/blob/master/examples/getVescValues...

The sample (and lib) does compile and upload just fine.

However, all I get is "Failed to get data!" message that seems to happens when there is a hardware communication problem.

VESC firmware 3.4 (i used the latest VESCT_tool to configure them).

• I tried making several UART cables. I check the 5v betwen 5V and GND. I used a multimeter to check connectivity between all 4 pins.
• I tried using 2 different VESC (all hardware 412 and fw 3.4, one is a focbox from enertionboards, the other is a chinese ESC from aliexpress that we realised when we receive it that it was in fact a VESC board). 
• I tried reverting TX/RX

Nothing worked.

How can I troubleshoot the issue?

Thanks