❔ Checking if a string only contains specified characters (Order doesn't matter)

class Navigation
    {
        public string Input { get; }

        private List<char> _allowedCharacters { get; }

        public Navigation()
        {
            AllowedCharacters = new List<char>() 
            { 
                '*', '/', '+', '-',
                '0', '1', '2', '3', '4', '5', '6', '7', '8', '9'
            };
        }

        public void UserInput()
        {
            bool invalidInput = true;

            while (invalidInput)
            {                
                Console.Write(">>> ");
                Input = Console.ReadLine();

                for (int i = 0; i < Input.Length; i++)
                {
                    if (_allowedCharacters .Contains(Input[i]))
                    {
                       if (i ==  Input.Length - 1)
                        {
                            invalidInput = false;
                            break;
                        }
                    }
                    else
                    {
                        Console.WriteLine("Invalid\n");
                        invalidInput = true;
                        break;
                    }                     
                }      
            }           
        }
    }