Trouble with Joining Tech Sales U Slack

Hi everybody,

I recently joined the course and have reached the part where I need to join slack to complete assignments. I am having issues joining. When I try and use the email I used to create my Tech Sales U account it gives me a message that states "The email address must match one of the domains listed below. Please try another email."

Can someone help clarify what I am doing wrong and how to successfully join Slack so I can move forward?