Adding custom png icon error

[PhilHolm]

I've been trying to add our own icons to a custom vector base map style that I've been working on but repeatedly receive a generic error message. The call to action button in the upload menu also seems strange, "Replace icon/pattern" I was expecting something like "Add item"  I've tried multiple browsers (Chrome, Firefox) and no dice. 

Not sure how to proceed and would appreciate a bit of help here. The icon I'm trying to update is a 64x64 png with a transparency background. 

[Andy-Green]

The Vector Tile Style Editor has an Edit icons and patterns option.  Then +Add where you can upload your png file for the new sprite.  You can then select that new item from symbol set for the feature you want to use it on.  There have been subsequent releases of the VTSE since your posting.  If the issue you initially reported still persists, repost the current status.  Thanks.