Hi @elano,
Sorry to hear that you are experiencing issues with creating an account.
Would it be possible for you to register for an API key at https://tinypng.com/developers?
After the registration, you can grab your API key at your account dashboard and paste it into your WordPress plugin. Can you please give this a try and see if it works?
If you are still running into issues, please don’t hesitate to send us a message at [email protected] accompanied with any screenshots of the issue.
Hope this helps!