Hi @kiran kumar m1,
I understand your question. Putting the visibility of the button aside for 1 second, rest assured that baseline configuration (Out Of Box) whilst the attachment icon is visible on the sidebar on the SOW to users regardless of the ticket state (Including closed), ACL's are implemented and it is not possible to add an attachment when a ticket is closed for ITIL users.
If testing as an admin, you will see that you can add an attachment, but this is based on admin access.
I do however understand your question and sadly to date, I have not see an easy way without digging into UI Builder as a way to achieve this sadly.
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Thanks, Robbie
