Apply automatically a coupon based on specific car

I am trying to automatically trigger a coupon to be applied in the cart specifically for when there are 4 items in the cart.

The coupon is pre-created in the Woocommerce back-end of the site "tasterbox"

I am using an amended version from this answer code:
Add WooCommerce coupon code automatically based on product categories

Here is my code version:

add_action( 'woocommerce_before_calculate_totals', 'wc_auto_add_coupons', 10, 1 );
function wc_auto_add_coupons( $cart_object ) {

    // Coupon code
    $coupon = 'tasterbox';

    if ( is_admin() && ! defined( 'DOING_AJAX' ) )
        return;

    // Initialising variables
    $is_match = false;
    $taster_item_count = 4;

    //  Iterating through each cart item
    foreach ( WC()->cart->get_cart() as $cart_item ) {
        // If cart items match 4
        if( $cart->cart_contents_count == $taster_item_count ){
            $is_match = true; // Set to true
            break; // stop the loop
        }
    }

    // If conditions are matched add the coupon discount
    if( $is_match && ! $cart_object->has_discount( $coupon )){
        // Apply the coupon code
        $cart_object->add_discount( $coupon );

        // Optionally display a message 
        wc_add_notice( __('TASTER BOX ADDED'), 'notice');
    } 
    // If conditions are not matched and coupon has been appied
    elseif( ! $has_category && $cart_object->has_discount( $coupon )){
        // Remove the coupon code
        $cart_object->remove_coupon( $coupon );

        // Optionally display a message 
        wc_add_notice( __('SORRY, TASTERBOX NOT VALID'), 'alert');
    }
}

However I can not get it to auto apply the coupon when there are 4 items in the cart. It seems like something simple to do, but I'm stuck.

Any help appreciated.

There is some little mistakes and errors in your code. Try the following instead:

add_action( 'woocommerce_before_calculate_totals', 'auto_add_coupon_based_on_cart_items_count', 25, 1 );
function auto_add_coupon_based_on_cart_items_count( $cart ) {
    if ( is_admin() && ! defined( 'DOING_AJAX' ) )
        return;

    // Setting and initialising variables
    $coupon = 'tasterbox'; // <===  Coupon code
    $item_count = 4; // <===  <===  Number of items
    $matched    = false;

    if( $cart->cart_contents_count >= $item_count ){
        $matched = true; // Set to true
    }

    // If conditions are matched add coupon is not applied
    if( $matched && ! $cart->has_discount( $coupon )){
        // Apply the coupon code
        $cart->add_discount( $coupon );

        // Optionally display a message
        wc_add_notice( __('TASTER BOX ADDED'), 'notice');
    }
    // If conditions are not matched and coupon has been appied
    elseif( ! $matched && $cart->has_discount( $coupon )){
        // Remove the coupon code
        $cart->remove_coupon( $coupon );

        // Optionally display a message
        wc_add_notice( __('SORRY, TASTERBOX NOT VALID'), 'error');
    }
}

Code goes in function.php file of your active child theme (or active theme). Tested and works.