The credentials asked for, are the credentials for the repo you are trying to access, not for your Gitkraken account, which is very confusing.
If you are using visualstudio.com, you would have to generate Git credentials. Do this by browsing to your project, click ‘Code‘ and then on the right top corner, there is a button ‘clone‘. Press that, a popup opens. In there, click ‘generate git credentials‘. Fill in a username/password combo and press ‘save git credentials‘. That combo will now work with GitKraken.