Unable to upload to STM32 Thing Plus

2 things that the guide mentions https://learn.sparkfun.com/tutorials/st … rogramming

As of this writing, SparkFun is using the DFU bootloader to upload code to the STM32 Thing Plus. In order to do so, you need to do the following:

1 Press and hold down the Boot button

2 Press and release the Reset button while continuing to press the Boot button

3 Keep pressing the Boot button until the code is uploaded (from software)

Note: If the blue LED remains dimly lit, it’s probably still sitting in the bootloader. After uploading a sketch, you may need to tap the RST button to get your STM32 Thing Plus to begin running the sketch.

Try that sequence for uploading; is the blue LED dimly lit after attempting?