When I click on the toggle text in the UI, I receive this error:

The mod Flow Configuration (2.0.6) caused a non-recoverable error.
Please report this error to the mod author.

Error while running event flow-config::on_gui_click (ID 1)
Expected sprite button or sprite.
stack traceback:
[C]: in function 'index'
__flow-config/control.lua:173: in function 'on_button_toggle'
flow-config/control.lua:283: in function <flow-config/control.lua:279>

I'm not super familiar with Lua, but changing line 282 of control.lua fixes this:

if event.element.parent == gui_instance.toggle_content and event.element.type =="sprite-button" then

Oh I had no idea you could get an event from clicking on a GUI Label, hah!
Fixed this by removing the label entirely cus it looks better imho (but ty for sharing your fix!)
Also updated the toggle button's design while I was looking at it, it'd been bothering me for a while anyway.

Thanks for the fix. The button looks much better!