You can see what happened upon screen visit using browser console and inspecting network requests there, however, it requires some technical knowledge.
Usually custom actions aren’t launched due to some mistakes in the payload. E.g. if you’re missing some parameter in payload, and due to that another server returns an error, you’ll never know about this issue. You can try to debug the action by attaching it to some button on the screen (and then you can see what happens after button press). Also you can get custom action responses when you run custom action on a button - examining these responses can give you a hint if the action has been executed or not.
As a side note - I’d not recommend putting custom actions on-screen-enter unless you 100% sure that it’s required. For example, if you have some button on this screen and you press it (without linking to another screen), all on-screen-enter actions will be re-executed.
If you need an action to occur when a user lands on a specific screen, I’d recommend using a countdown timer set to 3 seconds to perform your actions. You can make the countdown timer invisible/transparent by setting the opacity of the text/border colors to 0.
As @Victor had mentioned, custom actions are a little picky and may not work if the right parameters are not loaded.
I’ve noticed that on-screen-enter actions don’t always have enough time to load all of the proper data, whereas a countdown timer has enough time to pull all of the necessary information first.