@NusratKembhavi said:
sorry couldn't be authenticated with these credentials .
I am not able to use api
it is showing
sorry couldn't be authenticated with these credentials .
Need reply as early as possible

Where?
1 In a third-party APP
2 In an APP that you are developing
3 Using "Try it!" in Documents
4 Some other means
Please provide more details.

Check this link for possible error warnings and let us know which one you received.
https://developer.themoviedb.org/docs/errors

I am also having this problem, on an app im working on but even using the " Try it!" in the documentation. i pass my api-key into the try it and it gives error code 7 for any request.

@fhernandez.no said:
... but even using the " Try it!" in the documentation. i pass my api-key into the try it and it gives error code 7 for any request.

The "Try it!" option in DOCs it only works with the "Access Token Auth" option.
It doesn't work if you select the "API Key Auth" option.
Your API Key validation test is done using your Token.
https://developer.themoviedb.org/reference/authentication-validate-key
If your Token works then your API Key must also work.
If you want to test your API Key directly, follow the instructions below.

Take a Test
Using a computer, desktop or notebook.
On some mobile devices this test may not work correctly.
In the URL below, change THE_KEY to your API Key.
https://api.themoviedb.org/3/movie/550?api_key=THE_KEY
Use this example to do a search using a new tab or window in your browser.
You will receive the basic data of the Movie Fight Club (1999)
https://www.themoviedb.org/movie/550-fight-club
If it works, your Key is OK.

@fhernandez.no said:
I am also having this problem, on an app im working on

The problem must be in the code that is building your API Request, or something like that,
and is sending the Request to the TMDb Server.

It is very common to find people here with this type of problem.
A little mistake, a copy and paste with an extra space, or less character, an exchange of characters,
a quote left, use a dash when it should be underline, in short a typo and the answer can be that.
Even if the API Key is correct. The Requisition is that it has a little mistake.

I will place 6 API requests here. The first 5 with error.
You can see that the API Key is correct but the answer is Invalid API key or could not be found.

1 https://api.themoviedb.org/3/movie/550&api_key=THE_KEY  
2 https://api.themoviedb.org/3/movie/550/api_key=THE_KEY  
3 https://api.themoviedb.org/3/movie/550?api-key=THE_KEY  
4 https://api.themoviedb.org/3/movie/550? api_key=THE_KEY    
5 https://api.themoviedb.org/3/movie/'550'?api_key=THE_KEY  
6 https://api.themoviedb.org/3/movie/550?api_key=THE_KEY    

My suggestion is to check if there is any way for you to view the API Request that your APP is sending to the TMDb server.
Not the construction of the code, but the requisition built, final.
If possible, post the Request here.
If this is not possible, then you need to check in your code if there is a mistake, like the mistake in the examples above.
The error is usually in this segment of the API Request: ....?api_key=12345....