If you received an email after scheduling an interview that says, "Your calendar invite was not valid", this is likely because the interview kit URL included in the calendar invite is no longer a valid link. There are a few possible actions that could cause an interview kit URL to become invalid.
Your candidate might have been transferred to another job
When a candidate is transferred to a new role, the interview kit URL within the calendar invite is no longer applicable since it is specific to the previous job and interview.
Your candidate might have been recently merged
When a candidate is merged into another profile, the interview kit URL within the calendar invite might no longer apply because the interview kit URL might have changed due to the merging process.
The interview plan might have recently been adjusted, and the current interview was removed/edited
Sometimes during the interview process, members of your recruiting team might find it necessary to change up the interview plan due to process changes. Because of this, it could affect any current candidates' scheduled interviews and might adjust the interview kit URL in the process - rendering the calendar invite invalid.
You'll need to edit the calendar invite and replace the existing interview kit URL with the updated interview kit URL.