Hello,
Added a new member that is already on the group and there is no warning, and the logs show that the task was completed.
The behavior is by design. The operation is completed successfully in Adaxes, but there will be nothing done in AD itself as the account is already a member of the group.
Is there any way to add a warning message when someone tries to add a group member that already is member?
As a solution, you can use a business rule like below. It will cancel the operation in case the member being added is already in the group.