by cyoung » Wed Nov 06, 2019 10:45 am
Options can be added via a Surcharge (would be available on all orders, not just the ones with specific products), Ordering Options, or a separate product which you could present using the Cross-sell feature, or somehow else on the cart page using custom JavaScript, or you could even modify the add to cart button/form on the product page to add both items together.
If it really is a required fee and needs to be included for sure each time the product is ordered, then you could add it via a product's Handling Charge (handling charges get lumped in with shipping charges, they don't show as a separate line item), or make it the only available ordering option so it will automatically get added to the product price in the cart.