Wrongly configured Jinja expressions can result in an error when the action executes. This is easily identifiable by the phrase Error evaluating input: ... in the Detail tab, State info value, of the action that is in error state.
A common problem is the use of an undefined variable. In this case, the string would be something like:
```text
Error evaluating input: Undefined variables in '...
...
...
...': event.unknown_variable
```
where the `...` represents the whole body being evaluated, and `event.unknown_variable` (for example) is the variable being used but not defined.
