Error and warning messages should appear in a banner. In the case where there is more than one error or warning there should be a link at the end of the saying where you can click and a sheet will appear with all your messages there.
This banner will live below the global header
Single Error / Warning
Multiple Error / Warning
When there is more than 1 error or warning messages text will appear next to the warning with a link guiding you to all of your warning or error messages. If you only have one error or warning message you will see the message and be able to dismiss it