You can update an appointment status based on tags, which may be useful for your business and any automations you are running. Here's a recommended best-practice for updating appointment statuses based on tags within a Workflow, specifically related to the Invalid Status.
Part 1: Set up a tag for invalid Appointments.
Go to Settings > Tags
Create a tag called "Invalid Appointment".
Part 2: Create a tag-based trigger in Workflows.
Navigate to Automations, and add a new Workflow.
Add a new Trigger named "Contact Tag" and choose the filter “Tag Added” and then select the "Invalid Appointment" tag you created
Step 3: For the action, add “Update Appointment Status” and select “Invalid” as the status
Step 3: In the top right-hand corner, make the workflow active and save it.
Part 3: Using the Tag and Trigger
Step 1: When you have a contact with an invalid appointment, add the "Invalid Appointment" tag, and the workflow will run, updating their appointment status to "Invalid".