When actions are run, Drafts can log information and errors which occur in the action log. What, if any, is logged for a particular action depends on the configuration of the log level setting on the action.
The action log is helpful in troubleshooting errors which occur when running actions. Often the log will contain specific information about why an action failed - including information about what statement specifically failed in scripted actions.
To access the log, tap the log button at the top of the action list.