On-premise OAuth2.0 error: invalid_client: Authorization was attempted with an invalid client_id

We've build a integration with Maximizer, but now our client wants to connect their on-premise version and gets the following error:
invalid_client: Authorization was attempted with an invalid client_id

Create Lead (v2) with Process and Stage

Greeting Team,

Interaction Log API call is not pulling Emails

Hello,

Retrieving and Sorting Cases

I have an HTTP call that retrieves the cases associated with a specific AbEntry but I am trying add an OrderBy parameter but the results are still in ASC order.

Search for Phone Effectively

Greeting Team,

Mass Update (How to)

Greetings Everyone,

Mandatory Fields

The API sometimes fails to save a company because mandatory fields are missing, however it doesn't tell you which ones. How would you programatically find out which fields need to be completed?

API query using a PAT code is very slow

If I run the same simple query to retrieve all users via UserName/Password authentication in Postman the query takes 0.5 seconds to complete

Triggering Webhook from record changes made through WebUI

I was wondering if there has been any update regarding the webhook triggering with changes made though the WebUI instead of just being initiated by changes made through the API?

Is there a way to access the AuditLog with the API?

Since we are not working in an app that can send a request with the current user's PAT, I am trying to find a way to determine who made the most recent change to a specific field, either in an Opportunity or the Address Book. This way I can use the UID of that user to access their user information like email or phone number. I know I can have them enter their name in a UDF so that when the API gets the data , that filed is included, but I was hoping to remove that human element so that one user can't use someone else's name or make a typo, etc.