Hi @SebastianTh !
In regards to multiple calls, this sounds like a post we have here! http://community.retool.com/t/how-to-run-a-rest-api-query-for-each-item-in-an-array-and-return-all-results-together/2352
In regards to handling failure, we do have onFailure event handlers. They can be used to log the failures, or push the id of the failed queries into the temp state.
Here's a screenshot of how the temp state could be setup.
The value would be different of course! Here are our docs on Temp state as well: https://docs.retool.com/docs/temporary-state If you would need any more assistance let me know!