Hey Chadwill - Endpoint analytics is available for devices with a valid Microsoft Endpoint Manager license. (Note that some features, like Proactive Remediations, have additional license requirements.) More details here: https://docs.microsoft.com/mem/analytics/overview#licensing-prerequisites.
To verify that the customer was onboarded correctly, check the steps here: https://aka.ms/EAGetStarted. Then, if that checks out, we have some troubleshooting guidance here: https://docs.microsoft.com/mem/analytics/troubleshoot.
Perhaps the most important thing to realize is that most of the EA reports are event-based. For example, the Startup performance report includes data on boot and logon performance of enrolled devices. Since this data is calculated during a reboot, no data will be available in this report until enrolled devices have rebooted. This means that it can take several days for newly enrolled tenants to start seeing meaningful data in EA (and this is especially true for tenants with a very small number of devices).
After trying some of the troubleshooting steps above, if things still aren't looking right, I'd recommend opening a support ticket for more hands-on assistance: https://docs.microsoft.com/mem/analytics/get-support.