As you said the var number does not really impact anything as the number change but it remain consistent with the one set up in the firstPersonChar.
So the widget ref is correct.
I am just unable to use it the same way I use the one in the First PersonChar
FirstPersonChar Exemple
Actor Exemple
I tried to use it strait from the output of the event node
I also try to pass it trough a new var
Its all return the :
Object Widget Reference is not compatible with First person UI reference
At this point, I will continue to look for answer to that but my initial question have been answer correctly, Thanks!