c# – unity StartCoroutine() function does not calling function

Can some help my why does this code not executing I get the 2 debug messages from the CallRollDice function but nothing from the RollDice function.

public void CallRollDice() 
    {
        Debug.Log("clicked");
        StartCoroutine("RollDice");
        Debug.Log("ran");
    }
    private IEnumerable RollDice()
    {
        Debug.Log("called");
        
        int randomInt1;

        for (int i = 0; i < 10; i++)
        {
            randomInt1 = Random.Range(0, diceFaces.Length);
            diceImage.sprite = diceFaces[randomInt1];
            yield return new WaitForSeconds(0.05f);
        }
    }

When i researched the topic i found out that StartCoroutine function in some cases requires a function but in my case it is requires a string.

I am using unity version 2021.3.30f1 (lst)