Many thanks for sharing the screenshot of your workflow!
From looking into this, you might not need the Split in Batches node here as the HTTP request node will by default already run once for each item it receives from the Google Sheet.
So a workflow like this will run once for each item it receives from the Google Sheet:
In this example my Google Sheet looks like this:
The HTTP Request then runs once for each item:
Seeing your first HTTP might throw an error, you probably want to continue the execution for error cases as described here. You could then check handle the error with a subsequent IF node.
If an “item does not exist” error was thrown, you could then make an additional HTTP request as required. A recent post describing how to access data from more than one node ago can be found at How to pass data from 1 to 3? - #3 by mcnaveen in case it’s needed.
I hope this helps with getting started 