Use of local variable 'flipCard' before its declaration

I'm not a Swift guy but it appears you have that flipCard function declared inside the scope of the touchCard function. I would think it should be outside that function but inside the class. So my suggestion would be to move one of those closing curly braces to before the flipCard function.

You could also move the code for the func before its use in the IBAction, if you want to keep it inside.

    @IBAction func touchCard(_ sender: UIButton) {
       
        func flipCard(withEmoji emoji: String, on button: UIButton){
            if button.currentTitle == emoji {
                button.setTitle("", for: UIControlState.normal)
                button.backgroundColor =  colorLiteral(red: 0.9529411793, green: 0.6862745285, blue: 0.1333333403, alpha: 1)
            } else {
                button.setTitle(emoji, for: UIControlState.normal)
                button.backgroundColor =  colorLiteral(red: 1, green: 1, blue: 1, alpha: 1)
            }
        }
       
        flipCount += 1
        if let cardNumber = cardButtons.index(of: sender) {
            flipCard(withEmoji: emojiChoices[cardNumber], on: sender)     //Message: Use of local variable 'flipCard' before its declaration
        } else {
            print ("chosen card was not in cardButton")
        }
       
    }