Please let me share the troubleshooting list from the help center article.
If you are having trouble using the Figma mobile app, we recommend the following:
Make sure you’re using a supported device.
Make sure you have selected a top-level frame to mirror to your mobile device.
Make sure you’re logged into both the desktop version and Figma mobile app under the same account. You may need to log out and sign in again to confirm.
If you’re running into issues while previewing, you may need to force quit the app and restart it on your device.
If problems persist, we recommend uninstalling the app and downloading it again. Find the Figma mobile app in the Apple App Store or Google Play Store.