Issue with Java method validating String input yes or no

Having trouble with the getChoiceString method. If the user enters anything besides "y" or "n" an error message is suppose display. The problem is even if I type the correct response in the prompt it shows the error message.

Output I'm receiving

   //Ask user if they want to continue
   choice = getChoiceString(sc, "Continue? (y/n): ", "y", "n");
   System.out.println();    

    } //end while loop
  } // end main method

// Method to make sure user doesn't leave continue prompt null
public static String getRequiredString(Scanner sc, String prompt)
{
    String s;
    // Flag to exit loop
    boolean isValid = false;
    // While loop to validate user input on continue prompt
    while(!isValid){
       System.out.print("\nContinue? (y/n): ");
        s = sc.nextLine();
        if (s.isEmpty())
            System.out.print("Error! This entry is required. Try again.");
        else 
            // Exit loop
            isValid = true;
    }
    return prompt;

}

// Method to validate continue prompt input is either "y" or "n"
public static String getChoiceString(Scanner sc, String prompt, String s1, String s2){
    String s = "";
    boolean isValid = false;
    while(!isValid)
    {
        s = getRequiredString(sc,prompt);
        if (s1.equalsIgnoreCase("y"))
           System.out.print("Error! Entry must be 'y' or 'n'. Try again:\n");
        else 
            if (!s2.equalsIgnoreCase("n")) {
                System.out.print("Error! Entry must be 'y' or 'n'. Try again:\n");
            } else {
                isValid = true;
            }

    }
   return s;
}