Invoke Repeating Problem

I'm new to the whole invoke repeating part of code so naturally having issues with this. I'm trying to get it so that if I have my repeat toggle "ON" then after a specified time frame the message will be repeated. But I keep getting this:

 using UnityEngine;
 using System.Collections;
 using System.Text.RegularExpressions;
 using UnityEngine.UI;
 
 public class MorseCodePlayer : MonoBehaviour {
 
     public bool iSOn = false;
 
     public InputField inputFieldMCode;
     public    Text morseCodeDisplayText;
 
     public AudioClip dotSound;
     public AudioClip dashSound;
     public float spaceDelay;
     public float letterDelay;
     
     // International Morse Code Alphabet
     private string[] alphabet = 
     //A     B       C       D      E    F       G
     {".-", "-...", "-.-.", "-..", ".", "..-.", "--.",
     //H       I     J       K      L       M     N
      "....", "..", ".---", "-.-", ".-..", "--", "-.", 
     //O      P       Q       R      S      T    U
      "---", ".--.", "--.-", ".-.", "...", "-", "..-",
     //V       W      X       Y       Z
      "...-", ".--", "-..-", "-.--", "--..",
     //0        1        2        3        4        
      "-----", ".----", "..---", "...--", "....-", 
     //5        6        7        8        9     
      ".....", "-....", "--...", "---..", "----."};
 
     // Use this for initialization
         void Start () 
     {
         //morseCodeDisplayText = GameObject.Find ("MorseCodeDisplayText").GetComponent<Text> ();
         inputFieldMCode = GameObject.Find ("InputField").GetComponent<InputField> ();
         
         // H   E  L    L   O       W  O    R   L   D
         //.... . .-.. .-.. ---    .-- --- .-. .-.. -..
                 //PlayMorseCodeMessage("Hello World.");
                 PlayMorseCodeMessage ("");
     }
 
         public void MorseCodeField(string inputFieldString){
                 morseCodeDisplayText.text = inputFieldString;
         }
 
         public void RepeatMessage (){
                 Debug.Log ("Checking if Bool is On");
                 if (iSOn = true) {
                         InvokeRepeating ("repeat", 15f, 1f);
                         Debug.Log ("I will Invoke Repeat");
                 }
                 Debug.Log ("Confirming Bool Is On!");
         }
 
         //Repeat Message Being Sent after "X" time has passed.
         void repeat (string message){
                 Debug.Log ("I Will Submit Text");
                 StartCoroutine("_PlayMorseCodeMessage", message); //I thought this would just restart the message send Coroutine?
                 submitText ();
                 Debug.Log ("I HAVE Submited Text");
         }
                 
 
         public void readButton (string c){
                 
                 inputFieldMCode.text += c;
 
         }
 
         string messageToSend;
         public void submitText(){
                 messageToSend = inputFieldMCode.text;
         }
 
     
     
         public void PlayMorseCodeMessage(string message)
     {
         StartCoroutine("_PlayMorseCodeMessage", message);
     }
     
         private IEnumerator _PlayMorseCodeMessage(string message)
     {
         // Remove all characters that are not supported by Morse code...
         Regex regex = new Regex("[^A-z0-9 ]");
         message = regex.Replace(message.ToUpper(), "");
         
         // Convert the message into Morse code audio... 
         foreach(char letter in message)
         {
             if (letter == ' ')
                 yield return new WaitForSeconds(spaceDelay);
             else
             {
                 int index = letter - 'A';
                 if (index < 0)
                     index = letter - '0' + 26;
                 string letterCode = alphabet[index];
                 foreach(char bit in letterCode)
                 {
                     // Dot or Dash?
                     AudioClip       sound = dotSound;
                     if (bit == '-')    sound = dashSound;
                     
                     // Play the audio clip and wait for it to end before playing the next one.
                     GetComponent<AudioSource>().PlayOneShot(sound);
                     yield return new WaitForSeconds(sound.length + letterDelay);
                 }
             }
         }
     }
 }