How to attach properly icon to command in the custom toolbar?

I created new command in my custom toolbar and attached an icon to it (by Customize toolbar → Modify → Change icon). The new icon is visible in the customize window but is NOT Visible in the toolbar. How to make it visible?

Hello,

This took me a few to figure out & then test. After seeing you problem with my testing, I recalled another question like this. Have tested as answer states and does work. Please see answer in this post.

It works. Thank you so much

FYI credit to @Regina