Custom states are just like little post-it notes with useful values on for your page. You can stick them onto (pretty much) anywhere so you can find them later (like real postit notes, put them somewhere you can remember!). So if you set a custom state for a page to your Blockspring ID, it will then be available to use elsewhere on that page and workflows so you don’t have to go back and recalculate all the time.
We use them a lot for things like page state so “edit mode is YES” or temporary lists (users I am selecting to be friends).
In this case you want to set the state as the first thing you do in the workflow. So you are only doing it ONCE as emmanuel says. So instead of doing the API call in the create, you do it first, set a custom state to the blockspring alphanumeric.
Then set your thing’s id to that. Then use the state to display on the screen as well.
Hope that makes sense, can pop something in the forum app to show this if need be.