Device Name Change - "400 Bad Request" error - SOLVED

I've struggled through this for a while now.  The issue first arose about 3 months ago.

I always got the "400 Bad Request" whenever I tried to change the device name.  I could change the IP address with no trouble.

There's a long history in the Community (going back to 2017) but none of the solutions I found there worked for me. 

1. Tried different browsers

2. Tried Config save and Reset

I'm using AC3200 Nighthawk X6 model R8000

I was finally able to change the device name(s) by:

Using no spaces,

Using no _ (underbar)

I'm sure there are other forbidden characters, but avoiding these two gave me enough to manage understandable names.

hyphens are okay, btw.