Many thanks for any tips
I would focus less on simply lowering CPC and more on eliminating clicks that are unlikely to convert. Start by downloading your Search Term Report and identify terms that are spending money without producing orders. Lower bids on weak targets, add irrelevant or consistently non-converting searches as negatives, and move proven converting search terms into dedicated exact-match campaigns. Amazon itself recommends using search-term performance to increase bids on strong converters and reduce bids or add negatives for poor performers.
Also look carefully at placement performance. Top-of-search clicks can be considerably more expensive, so don’t use large placement adjustments unless the conversion rate justifies them.
Finally, CPC is only half of the equation: improving your main image, price, reviews, listing quality and offer can increase conversion, meaning the same number of clicks produces more purchases. I would rather pay $1 for a highly relevant click that converts than $0.40 for traffic that never buys.