Why there ara custom status that cannot be added to a board (agile) column?

[Marta Lopez Reyes _UOC_]

I have some custom status added to an agile board column and there is a warning with this text:

"this status is not avaiable in any of the workflows used by this board..."

[Nic Brough -Adaptavist-]

The message is what it says it is. 

You've got a status that is not used by any of the workflows in the projects that the board is selecting issues from.

For example, status "confirmed" is used by workflow "bug".  Workflow "bug" is only used by bugs in project ABC.  Your board filter says "issues in project B"