Not every shift on your roster is assigned to you directly. Some are opened up to a group of eligible staff at once, so that any one of them can take it. This is called shift bidding, and this article covers how it works from your side.
When your employer creates an open shift, it goes out to every employee eligible for it, based on things like location, availability and role. You are notified the same way as for any other shift.

If you are eligible, able to work the shift, and want it, accept it the same way you would accept any other shift. Genrally - whoever accepts first is assigned the shift.

There is no penalty for not responding to an open shift you do not want or cannot work. It simply stays open until someone else accepts it, or your employer reassigns it directly.
If you were assigned an open shift you did not accept, or you believe you should have been eligible for one that did not reach you, please raise this with your payroll contact rather than Tempus Support directly.