How to add Confluence (on-prem) as a datasource in Search & Intelligence

I have been trying to connect our on-prem Confluence instance to our M365 environment for over a month.

I have been using the following KB as a guide: https://video2.skills-academy.com/en-us/microsoftsearch/confluence-onpremises-connector

Every time I create the application link using OAuth 2.0 (Which according to the guide is recommended)

The guide is very misleading as it references Appliction links photos and steps from Atlassian, but it very old. The new version does not even have settings for 1.0 only 2.0.

MS support thus far has been wildly unhelpful.

I get the following error whenever I try and authenticate:

{
  "error": {
    "details": [
      {
        "code": "InvalidConnectionCredentials",								
        "message": "Invalid credentials obtained. Please check the key and its format."
      }
    ],
    "code": "AccessDenied",
    "message": "The client doesn't have permission to perform the action."
  }
}