Please don't use the issue tracker for questions. When you use the issue tracker for questions, you limit the number of people who will see your question and thus you limit the number of people who will reply to your question.
Use the Jenkins user mailing list or the Jenkins chat channels for questions. Instead of 1-3 people seeing your questions, 10-100 people will see your question and may be willing to assist.
In your example, you're using the HTTP protocol to attempt to open the remote repository, but it appears from the error message that you're using a private key credential. HTTP and HTTPS access to a remote repository require a username/password credential, not a private key credential. Private key credentials require SSH access to the remote repository.
Please don't use the issue tracker for questions. When you use the issue tracker for questions, you limit the number of people who will see your question and thus you limit the number of people who will reply to your question.
Use the Jenkins user mailing list or the Jenkins chat channels for questions. Instead of 1-3 people seeing your questions, 10-100 people will see your question and may be willing to assist.
In your example, you're using the HTTP protocol to attempt to open the remote repository, but it appears from the error message that you're using a private key credential. HTTP and HTTPS access to a remote repository require a username/password credential, not a private key credential. Private key credentials require SSH access to the remote repository.