To resolve the issue of not being able to join Microsoft Teams, follow these detailed steps:

1. Check Your Internet Connection
Ensure that your internet connection is stable. You can test this by visiting other websites or using other apps that require internet access.

2. Clear App Data
Sometimes, clearing the app data can resolve sign-in issues. On your iPad:
- Navigate to Settings.
- Scroll down and find the Teams app.
- Tap on the app to view its settings, then select "Clear Data."

3. Reinstall Microsoft Teams
Although you've mentioned trying this, ensure you follow the correct steps:
- Press and hold the Teams app icon until it starts jiggling.
- Tap the “X” to delete it.
- Go to the App Store, search for Microsoft Teams, and reinstall it.

4. Update iOS
Make sure your iPad is running the latest version of iOS. Check for updates by:
- Going to Settings > General > Software Update.
- If an update is available, download and install it.

5. Check Microsoft Account Permissions
Verify that your Microsoft account has the necessary permissions to join teams:
- Log in to your Microsoft account through a web browser.
- Ensure that you have access to the teams you are trying to join.

6. Enable Permissions for Teams
Ensure that Teams has the necessary permissions to function:
- Go to Settings > Teams.
- Check if it has permissions for Camera, Microphone, and Notifications.

7. Join Through a Different Method
If the app fails, try joining a meeting through the web version:
- Open a web browser on your iPad.
- Go to teams.microsoft.com and sign in. Try to join the meeting from there.

8. Contact Support
If none of the above solutions work, consider reaching out to Microsoft Support for further assistance. You can do this through the app or by visiting their official support page.

For more details on troubleshooting Microsoft Teams connectivity issues, you can visit:
- Microsoft Teams app not allowing me to join meeting or sign in - [learn more]
- I can't join a meeting in Microsoft Teams - [learn more]

These steps should help you resolve the issue effectively. If you continue experiencing problems, further investigation may be needed to identify any underlying issues.