When you encounter an `Invalid username or password` issue in Git, it typically indicates an authentication problem when trying to interact with a remote Git repository. Here are the key steps to resolve this issue using GitBash [1]:
1. Check Your Credentials: Double-check the username and password you are using. Ensure that they are correct.
2. Use Personal Access Token (PAT): If you have two-factor authentication (2FA) enabled on your GitHub or Git hosting platform, you can't use your password directly. Instead, you should use a Personal Access Token (PAT) as a password. Generate a PAT on your Git hosting platform, and use it in place of your password.
3. Update Your Password or Token: If you suspect that your password or token might be incorrect, reset it in your GitHub account or the service hosting your remote repository. Then, update your credentials in your local Git configuration:
* For GitHub, go to your GitHub account settings, and under `Security`, update your password or generate a new personal access token if you were using one.
* For other Git hosting services, follow their respective password or token reset procedures.
4. Clear Cached Credentials: Git often caches credentials for a period of time. Clearing these cached credentials may help resolve the issue. You can do this using the following commands:

    git credential reject
    git credential reject https://github.com

Replace `https://github.com` with the URL of your remote repository.
4. Update the Remote URL:
* Verify that the remote repository's URL is correct and that it uses the HTTPS or SSH protocol as appropriate. You can check the remote URL using the following command:

        git remote -v

* If necessary, you can update the remote URL using the git remote set-url command:

        git remote set-url origin https://github.com/username/repo.git

5. Check 2FA Settings: If you are using 2FA, ensure it is correctly configured on your Git hosting platform, and that your PAT is generated with the necessary permissions.
6. Update Git Credentials Helper: If you are using a credential helper, make sure it is up to date. For example, on Windows, you may use the Git Credential Manager. Check for updates and ensure it is configured correctly.
7. Use SSH Authentication (Recommended): Consider using SSH keys for authentication instead of username/password or tokens. SSH keys are more secure and convenient for Git operations. GitHub provides excellent documentation on how to set up SSH keys: Connecting to GitHub with SSH.
8. Check Repository Access Settings: Ensure that you have the necessary permissions to push or pull from the remote repository. If it is a private repository, make sure you are added as a collaborator or have the required access permissions. Check with the repository owner or administrator if necessary.
9. Two-Factor Authentication (2FA): If you have 2FA enabled on your GitHub account, you should use a personal access token instead of your password for Git operations. Generate a PAT and use it in place of your password.
10. Retry the Operation: After making the necessary changes and ensuring your credentials are correct, try the Git operation again (e.g., git push or git pull) to see if the issue is resolved.

By following these steps, you should be able to resolve the `Invalid username or password` issue in GitBash and regain access to your remote Git repositories. If you continue to face issues, it is important to double-check your credentials and verify that your authentication method (password or PAT) matches the security settings of your Git hosting platform.