posting an update here as i also posted on the kodi forum.
anyone trying to get unsplash to work, you need to do the following;
create an unsplash account, then navigate to the dev section and create a new app. don't need to publish anything just get to the point where you get App ID and Access Key (API Key) and secret code.
from there, enter the API key in the settings on unsplash in kodi. also i am using the beta repo for installing the addon vs the official kodi repo.
i am having one issue which i am trying to solve, the images aren't rotating every 30 seconds for me
hope this hepls for anyone searching