Error “The selected function was provided the incorrect number of arguments”

I have the following expression and keep getting an error message that says: "The selected function was provided the incorrect number of arguments"

concat(if(selected( danger_signs, 'convulsions_unconsciousness'), "Convulsions or Unconsciousness,", ""), if(selected( danger_signs, 'headaches_vision'), "Headaches or Blurred Vision,", ""), if(selected( danger_signs, 'vaginal_bleeding'), "Vaginal Bleeding,", ""), if(selected( danger_signs, 'vaginal_discharge'), "Vaginal Discharge,", ""), if(selected( danger_signs = 'swelling_face_hands'), "Swelling face or hands,", ""), if(selected( danger_signs, 'fever'), "Fever,", ""), if(selected( danger_signs, 'breaking_water'), "Breaking Water,", ""), if(selected( danger_signs, 'abdominal_pain'), "Abdominal Pain,", ""), if(selected( danger_signs, 'excessive_tiredness'), "Excessive tiredness,", ""), if(selected( danger_signs, 'lower_leg_pain'), "Lower leg pain,", ""), if( urinary_urgency = 'yes', "Urinary Urgency,", ""), if( referral_reason_other = "", "", "Other:"),  referral_reason_other)