So the BR would run when the record is updated and the HR Service is Matching your service

1) in your BR you cannot use producer object; you need to use current

2) gs.log() won't work in scoped application and your script will break so use gs.info()

(function executeRule(current, previous /*null when async*/) {
    
gs.info('ITP HR service ' + current.hr_service);
    
    var transfer_person = current.variables.employee_name;
    gs.info("Abira transfer for " +transfer_person);
    var position = current.variables.new_position;
    gs.info("Abira Position " +position);
    
    var effecdate = current.variables.effective_date;
    gs.info("Abira date " +effecdate);
    var country = current.variables.transfered_position_country;
    gs.info("Abira country " +country);
    var loc = current.variables.transfered_position_location;
    gs.info("Abira location " +loc);
    
        var req_body='{'+
        '"effectivedate":"'+effecdate+'",'+
        '"trapercountry":"'+country+'",'+
        '"location":"'+loc+'",'+
        '"Position":"'+position+'",'+
        '}';
gs.info('ITP payload details'+req_body);

})(current, previous);

Regards
Ankur