So I am working on getting a weather (Button) card to show specific icons of my choosing according to the openweathermap_weather_code. I have a group of icons at /local/community/weathericons/ I can directly access the icons a http://localip:8123/local/community/weathericons/storm.png so I know my path is correct. here is my yaml that I am trying in a button card
I have not worked much with the button card, but I know the path on the HTTP link is different than the ones for the file link and many mess it up.
I suggest you remove your template in the image section and start with just a direct path to the file and when that works, then you advance your code to a template.
Ask on the Github page for the button card you use or see if the author have a thread in the forum somewhere.
I know that the author is pretty active, so the chances of an answer is pretty high.