The background report displays as unavailable when the applicant does not enter a social security number. If a user does not have an SSN they can still submit an application, go through ID verification, and request a credit report, but will not be able to request or create a background check report. If your renter wants to include their SSN to generate a report, please see this article on how to help them troubleshoot.
Other potential reasons include: the report being in dispute, there is a security freeze on the background report, or other technical issues. For more information on this, please visit this article on how to report an issue with viewing a background check.