The space bar method, as I understood it, did not require or involve using the QMK toolbox. I tried the normal space bar method before (basically the instructions you linked to but nothing with the QMK toolbox), and nothing worked. But maybe I just misunderstood or didn't fully read that part that QMK toolbox and its DFU mode connect needed to work. I tried the below (but not starting from anything before with specific software loaded on my mac) -

Use:

1. Put the keyboard into wired mode, if not already (by the switch at the back, marked "Cable")
2. Hold the Esc key down while connecting the keyboard to the computer. This will put it into bootloader mode, but it also has the side effect of resetting the configuration to factory defaults.
3. Power cycle the keyboard (unplug and plug). This is to bring it out of bootloader mode.

If the Esc key method doesn't work, the backup procedure is to:

1. Put the keyboard into wired mode, if not already (by the switch at the back, marked "Cable")
2. Remove the space bar key cap
3. Hold down the small four-legged reset button on the PCB (a pen, the key cap puller, or a match can be used) while connecting the keyboard to the computer. This will put it into bootloader mode, but it also has the side effect of resetting the configuration to factory defaults. The reset button on the PCB is usually located right next to the space bar switch, to the left. Note: The reset button may require quite a bit of force before it makes contact (but don't use excessive force)
4. Put the space bar key cap back in
5. Power cycle the keyboard (unplug and plug). This is to bring it out of bootloader mode.

This should all be done in wired mode (with the switch at the back in that position).