@thefrostking98 said:
Having issues with connecting webhooks
I'm very new to API so I don't know much about anything.
I've been attempting to connect my web hooks from Zapier to retrieve trending/popular movie info and have that info transferred to a Google docs sheet.
Everytime I put in the API information I get either a 403 or 401 error.

Is this error message, 401 or 403, coming from the TMDb server or from your system?
If it is coming from TMDb, please provide the code.

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31      401     Account disabled: Your account is no longer active.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.  

8       403     Duplicate entry: The data you tried to submit already exists.
45      403     This user has been suspended.

Is there an in-depth explanation on how log-in/authentication works for this API?

Are you using API Key (v3) or API Read Access Token (v4)?
We have API documentation.
https://developer.themoviedb.org/docs/getting-started
You might want to take a look at it.
https://developer.themoviedb.org/docs/authentication-application

Does anyone have advice on connecting webhooks?

I can't help you with that.