3251891 - API call getting error "already exists in the system" - Onboarding

When trying to make an API call to make the candidate Hired in the system, the error is shown: "request could not be completed because the "userName" value provided for userName already exists in the system. Please provide a unique value."

SAP SuccessFactors Onboarding

User already exist.

Please make sure before make the call the user is unique, the same cannot exist in the system.

Username, User, Id, API, Call, Request, Value, Exist, System, Unique, Onboarding, ATX, Integration , KBA , LOD-SF-OBX-IAS , IAS User Authentication , Problem