Could you clarify if the WebUI does not load up, or does it not accept the credentials?
Have you tried logging in via SSH? Command Line Interfaces RutOS - Teltonika Networks Wiki
If you are able to login via SSH, please post a screenshot of the information you can see in the Putty window.
In order to resolve the issue that you are currently experiencing, additional provision of further confidential details is required. Hence, it is recommended that you reach out to your designated sales manager or the reseller from whom you acquired the device in question. They will be able to assist you in addressing this matter more effectively.