This is the standard troubleshooting procedure for "Why wasn't this scheduled?".

Option A is correct.If there is white space, but the optimizer didn't use it, there is likely aRule Violation(Hard Constraint) preventing it (e.g., The resource is missing a Skill, the Territory doesn't match, or the Travel Time is too long). Manually dragging the appointment to that specific spot on the Gantt triggers the rule validation logic, and the console will pop up a "Rule Violation" message telling you exactlywhichrule failed (e.g., "Match Skills Rule Violation").

Option Bhelps findvalidslots, but it doesn't explain why thecurrentwhite space is invalid.

Option Caddresses scoring (Objectives), not hard constraints (Rules). If there was space, the objectives would just give it a low score, not prevent scheduling entirely (unless the score was 0, but Rule Violations are the more common culprit for unscheduled work).