@raulsm said:
My TMDB API Key doesn't work
Hello, I've trying to use my TMDB Key API to create a movie tracker app
but the API throws this error:
Invalid API key: You must be granted a valid key.

Thank you in advance

This error may be caused by your API Key being invalid or some small error in the code you are writing for your APP.

You can check if your API Key is working properly.
Just replace THE_KEY with your Key and open it in a new tab or window in your browser.

https://api.themoviedb.org/3/movie/550?api_key=THE_KEY  

If it's working then the problem isn't with your API Key.

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....