Hello! @Seller_0zW6D6gLF07bo

This is Roberto. I'd like to contribute to your post and hopefully clarify the difference between these terms.

Promo rebates refer to discounts or coupons provided to the customer by Amazon, these discounts are fully funded by Amazon on certain products and offers free shipping to buyers after a certain threshold.

Note that these rebates don't have an impact in your sales proceeds, you can read more about this in the articles below:

Discounts Provided by Amazon

Order with Free Shipping by Amazon

If you have doubts on these rebates, I highly encourage you to raise a case with our Seller Support team.

Cost of Advertising or Advertising cost of sales (ACOS) refers to the percentage of direct sales that you have made from sponsored ads campaigns. See an article below that expands on this topic:

Advertising cost of sales (ACOS)

Let me know if you have other questions that may need further clarification.

Regards,

Roberto