src/Checkout/Checkout.php
public function validateMember($member)
    {
        if (!CheckoutConfig::config()->membership_required) {
            return true;
        }
        if (empty($member) || !($member instanceof Member)) {
            return false;
        }

        return true;
    }
public function validateMember($member)
    {
        if (!CheckoutConfig::config()->membership_required) {
            return true;
        }
        if (empty($member) || !($member instanceof Member)) {
            return false;
        }

        return true;
    }
Checks if member (or not) is allowed, in accordance with configuration