Coldbusted.org allows only one code to be used per order. This includes both automatic and manually entered discount codes. If an order automatically applies a discount code you cannot remove it and manually enter a different code.
No stacking, codes cannot be combined, and automatic codes cannot be used with additional codes. Free shipping codes cannot be used with additonal codes.
You will not have the option to use a discount code when paying with Google Pay and Apple Pay as these checkout methods bypass the standard Shopify checkout process.