Hello,
Sometime we are unable to remove/delete domain from the Plesk control panel. Do not worry, there is another way to remove it and that is the Command Prompt (backend). Please check the example given below.
=================>>>
root@ ~]# /usr/local/psa/bin/domain -r domain.org
SUCCESS: Removal of 'globalsiege1.org' complete.
[root@ ~]#
=================>>>
Thank you,