You may not have a compatible device. Call of Duty Warzone Mobile requires a device with at least 2GB of RAM and 3GB of storage space. You may not have the latest version of the Google Play Store app.
If you're signed in but having trouble connecting, check your system's status page for connectivity alerts, maintenances, or other factors indicating that servers are not fully operational. If there are issues with your system's servers, you might experience connectivity issues until they return to full operation.