It wasn't an Amazon promotion, just a Bookbub ad pointed at Amazon. It did well on CTR and what by industry standards is a good conversion rate. (CPM $9.84, clicks 482, CTR 2.37. I calculate it had about a 4% conversion rate) I still only did somewhat better than breaking even. Truthfully, I think the point of the whole exercise was to make me feel better by having something selling. I know that is silly but we are human after all.
How it happened, one of my novels is temporarily price reduced on Apple for an Apple run promotion, which I did not expect Amazon to match, but they did so I thought, 'Well hell, I'll throw a few hundred dollars at BB ads to advertise the Amazon price reduction." I had been turned down for a BB promo so used part of the money I would have used for that. So I ended up about $20 to the good. At least I didn't lose money on it and that cannot always be said for BB ads.