QMK Toolbox says flash was successful but no keys work...how to debug

[vectorfrog]

I'm a newb.  I've been following a youtube video on getting my Let's Split olkb set up using qmk toolbox.  Everything looks good in qmk toolbox.  When I hit reset, the signal is picked up, when I flash my hex file, I get a success message.  But then, why I start typing on the keyboard, none of the keys work.  I'm totally confused, and I don't know how to debug.  Are the switches not properly contacting with the PCB?  If so, how do I confirm that?  Is there some special step I need to take because I'm on a Mac?  I can't find a troubleshooting guide that addresses this stage of a successful flash, but the keystrokes not registering.  Any tips or guides out there for this use case, or are there any services where I can pay someone to help me debug this?

Here's the tutorial that I'm following: 

t=359s

[Sup]

Before flashing did the keys work? Most pcb's come pre flashed. Since all keys don't work it's probably the hex file.

Since you are this far into his tutorial I assume you have a working QMK environment. If your board is supported you should find the keyboard under the creators named folder and compile a default hex file and flash it from the command line. If that doesn't fix your issue then, your board could be faulty.

[Leslieann]

I've had it work right away then not work after unplug-plug and I've had some that needed an unplug-plug to work.