Script Image: not using environmental variable for path

I am trying to use scripts to pull an image for a button from a file using an environmental variable in the path without success. I have verified that the path, using the explorer, is correct.

This is the path with the environmental variable. It correctly calls up the image when I enter it into the explorer.

%thumbs%\tn\T01_P02_B01_C05.jpg

here is the CMD echo:
C:\Users\[redacted]>echo %thumbs%
E:\Dropbox\G - Projects\FFoB_Project\B01_Elements\Footage_Elements\1B_FFoB_Video_Thumbs

This does not work on the button:

[(init){image:%thumbs%\tn\T01_P02_B01_C05.jpg}]

But this does:

[(init){image:E:\Dropbox\G - Projects\FFoB_Project\B01_Elements\Footage_Elements\1B_FFoB_Video_Thumbs\tn\T01_P02_B01_C05.jpg}]

Is there something I am doing incorrectly when I use the environmental variable?

Any help would be appreciated.

For some reason unknown to me, the Stream Deck software needs to be restarted after creating the environment variable. After that, it will work.

This makes sense. When you have a CMD open and you make a change to an environment variable, you have to open a new CMD window for the env variable to take effect. 

Thanks. This is working perfectly now.