Overview
We are trying to get API Authentication working for our Jira Cloud instance.
So far we have tried to call a simple GET endpoint to get the details of a ticket in both Salesforce Dev Console and in Restlet. Every time we try it, though, we get a 404 error. When trying to call the endpoint in Restlet if I'm logged into Jira in the browser at the time, it will work presumably because it uses my session credentials in the browser.
It seems very clearly to be an authorization issue of some kind, but we cannot figure out what is failing because we don't get much information in the response.
Details
Endpoint: "https://<OurSandboxUrl>.atlassian.net/rest/api/3/issue/<IssueKey>"
Header: "Authorization: BASIC <Base64EncodedUserNameAndAPIToken>"
Method: GET
Other Things We've Tried
Went through our Project permissions and added the user we're trying to authenticate with to have permissions for every possible action one can perform on an Issue/Ticket.