...so just for the record and to complete the loop.
@Russ just IM'd me and resolved the issue.
Amazing service and phenomenal customer journey

In brief, to reboot/restart your Windows 10 PC from an iOS Home Screen button click, do the following:

1. Install TriggerCMD Agent
2. Sign up/in to IFTTT
3. For the If bit: select Button Widget
4. For the Then bit: select webhooks and enter the following:
   i. URL: https://www.triggercmd.com/api/IFTTT?trigger=Reboot in 10 seconds&computer=R1
   ii. METHOD: POST
   iii. CONTENT TYPE: x-www-form-urlencoded
   iv. BODY: token=XYZ

Notes:
There are spaces in "Reboot in 10 seconds"
My computer name is "R1"
<obviously <XYZ> is my token

To add the button widget to your iOS home screen:

1. Tap the share icon (square with the up arrow)
2. Tap "Add to Home Screen"
3. Tap "Add"
4. Enjoy

oops - that was for @Russ

Hi,

Am super-lovin' this

However, and trying to configure an IFTTT Button Widget to kick-off a webhook to my PC (PC name R1) to run the Reboot in 10 seconds command, but keep getting 401 errors - please help.

Am at the webhooks config page in IFTTT and entering the following:

URL: https://www.triggercmd.com/api/IFTTT?trigger=reboot&computer=R1
METHOD: POST
CONTENT TYPE: x-www-form-urlencoded
BODY: token=XYZ&params=russ.txt

<obviously <XYZ> is my token

What am I doing wrong please ?

Thanks so much,

Dan