A. 1. Reset your password: If you are having trouble logging in, try resetting your password through the 'Forgot Password' option in the app.
2. Clear app cache: Go to Settings > General > iPhone Storage, find GTWorld, and tap on it. If there's an option to 'Offload App', do that to clear some cache without losing data.
B. 3. Ensure correct credentials: Double-check that you are entering the correct username and password, and ensure that Caps Lock is not on.