I have been trying to make changes on my watch from phone app and I don't see any charges. I've tried more than several times to change watch face and nothing.
Here is more information on how to download and customize watch faces. https://www.samsung.com/us/support/answer/ANS00080308/
Does the watch show up in the Waerable app? I used to have issues, was the watch plugin required by the Wearable app. Once properly installed, watch faces could be changed using the app.