@HeinzPaulBinju said:
Invalid API Key

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.

When there is a problem, the TMDb Server sends a message.
Can you tell which message the server sent?
Here is a list of possible messages:
https://developer.themoviedb.org/docs/errors

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

i generated a new key and then tried testing out the "try it out" section but then its showing invalid API key ,

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.
It is a birth defect since the migration to this service.
I don't know if it can be fixed. I'm not a programmer.
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.

Travis Bell say:

This is entirely controlled by ReadMe.
I've asked them to add proper support for two different auth types (bearer token and query params) but they won't commit to it.

Last question

I even tried using it within my personal project and it still returns invalid API key in the console.log

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....