MTDB is a third party program.
https://mtdb.vebto.com/
TMDb cannot support third party programs.
What I can suggest is that you do a test to check if your KEY is valid and if there is any restriction on your ISP service.

Take a test.
Click to go to your Profile > API: https://www.themoviedb.org/settings/api
At the bottom of the page, below, you'll find the Example API Request.
https://api.themoviedb.org/3/movie/550?api_key=[MY_KEY]
Use this example to do a search using your browser.
If it works, your Key is OK.

When there is a problem, the TMDb Server sends a message.
Here is a list of possible messages:
https://www.themoviedb.org/documentation/api/status-codes
Can you tell which message the server sent?

If it does not work, let us know right here.

If you are in India, probably the problem is with the Internet Service Provider or ISP.
See here: https://www.themoviedb.org/talk/5c3928d70e0a26444200460f