If you are adding a repository in 'Source Code Management' section of Jenkins and after adding correct username and password as a credentials, it is still showing 'Failed to connect to repository' error then this solution might work for you.
Solution :
check the character '@' in your username and password. I would suggest you to not use email as your git username. To remember username, people use complete email as a username. If your email is john.doe@mail.com, I would suggest you to not use 'john.doe@mail.com' as a username. You can use john.doe or if it is not available, you can use any number after it.
Similarly you should not use '@' in the password too.
After replacing '@' with other special character like '_', you should try to connect git repository from Jenkins again.
