In Florida, all Process Servers serving non-enforceable process must be licensed. In order to serve a Summons and Complaint you must have a valid process serving identification. This identification must be presented when serving process and also the Process Server identification number must be listed on the Affidavit of Service.
Not all states require a process server to be licensed. However, some states require that process servers be registered in their county or state, or appointed to serve in a specific county.