@carbon6 Good that you have been able to upload the firmware.

It might be useful for the future or for others so regarding the use of stm32flash

You can download the stm32flash directory from this github repo:
https://github.com/Ebiroll/RAK811_BreakBoard

There is also a windows version of the stm32flash tool in the stm32flash directory.

You can also find explanation about how to use this tool in the github readme.