When someone adds a product to their cart, with a quantity of 1, the rate was being calculated. But if we changed the product quantity to 2, the rate was doubled. It seems to be working as if the products will be shipping separately? They shouldn’t get charged for the shipping rate twice, only once. How do we make it so that it calculates this correctly and only charges them once for the shipping?
This issue can be easily resolved by changing the parcel packing option.
You must have selected “Pack items individually” in Parcel packing option (in plugin settings).
Kindly change that to “weight based“, because you are in need of weight based calculation (as I can make out from your last query).
Pack into boxes with weight and dimensions: If packing items individually does not suit to your business, then you can define required box sizes under Box Dimensions section. All the cart items are packed into custom boxes defined in Box Dimensions settings. The best fit box is auto chosen from the defined boxes.