Approval Workflow : Guideline to "configure rule conditions"

Hi team
I configured a Job Offer Approval workflow and I'm trying to add a Rule condition at the beginning as requested by the client.
I mean, the condition considers to trigger the Job Offer Approval workflow JUST IN CASE the field "Assignment Category" is equal to "Staff e Operativi non soggetti a bacino".

I tried to set (Proposed Assignment Details.Assignment Category != "Operativi soggetti a bacino") but the Job Offer approval workflow is triggered also if the Assignement Category field is populated with the other value "Operativi soggetti a bacino"

Trying with the rule condition involving the "equal" function, the approval workflow doesn't work in any case