Hi @tacolegs2004, hard to tell without seeing more information, but it looks like whatever variable you are using for the api_key is undefined when you use it.

If you are reading the key from an env file, then see these discussions about what can go wrong:

https://stackoverflow.com/questions/49579028/adding-an-env-file-to-a-react-project

https://stackoverflow.com/questions/48378337/create-react-app-not-picking-up-env-files

@tacolegs2004 said:

When I try the api out in the browser using my api key, I receive the correct data. However, when I fetch that link in my code, I receive that error. I am running my code in NextJs13 and Typescript.

It would help to know which of the 401 error responses you are getting.

See the list of TMDb server error warnings here.
https://www.themoviedb.org/documentation/api/status-codes
In your case:

Code    HTTP    Message  
3       401     Authentication failed: You do not have permissions to access the service.
7       401     Invalid API key: You must be granted a valid key.
10      401     Suspended API key: Access to your account has been suspended, contact TMDb.
14      401     Authentication failed.
16      401     Device denied.
17      401     Session denied.
30      401     Invalid username and/or password: You did not provide a valid login.
31      401     Account disabled: Your account is no longer active. Contact TMDb if this is an error.
32      401     Email not verified: Your email address has not been verified.
33      401     Invalid request token: The request token is either expired or invalid.
34      401     The resource you requested could not be found.
35      401     Invalid token.
36      401     This token hasn't been granted write permission by the user.
38      401     You don't have permission to edit this resource.
39      401     This resource is private.