General
Observe the notes in chapter Ausgehende Kommunikation (von Connect) and in the chapter Kommunikation Connect -> Jira (allgemein).
HTTP Error 403 (Forbidden)
Since the beginning of the year, logging in via Basic Authentication no longer works with a simple Jira user and their password. Instead, an API key must be generated. You can find more information about this under the following link:
https://developer.atlassian.com/cloud/jira/software/basic-auth-for-rest-apis/In Connect, if the email address of an Atlassian user (as the user) is specified instead of the user and password, and a valid API key is specified as the password, authentication works as desired.