Hi there! I'm sorry to hear that you're having trouble signing into the Concepts app on your Galaxy Tab S8. Let’s work together to get this sorted out.

First, can you let me know if you're receiving any specific error messages when you try to sign in? It would also be helpful to know if you’ve tried anything already, like restarting your tablet or checking your internet connection.

In the meantime, here are a few steps that might help resolve the issue:

1. Restart Your Device: Sometimes, simply restarting your tablet can refresh the app's connection and allow you to log in.

2. Check Your Internet Connection: Make sure you’re connected to a stable internet connection. You might try moving closer to your Wi-Fi router or switching to mobile data to see if that helps.

3. Update the App: Ensure that you have the latest version of the Concepts app installed. You can check for updates in the Google Play Store.

4. Clear App Cache and Data: To do this, go to Settings > Apps > Concepts > Storage, then tap on Clear Cache and Clear Data. This will reset the app without losing your saved work. After that, try signing in again.

5. Reinstall the App: If none of the above works, uninstalling and reinstalling the Concepts app can sometimes fix sign-in issues.

If you continue to have difficulties after trying these steps, let me know, and I can look up more specific solutions for you!