Okay, this is why I enjoy carping so much. It's not just throw a lure, soft plastic, switch, switch, throw, throw, throw. There's strategy involved, understanding the fish, its environment, habits, food sources, etc.
Here in the US, we default to sweet flavors, corn, grains. Boilies are not a thing (mostly). I do believe they have to sense a flavor as I've seen many carp pick up my offering and spit it out, or just move on while eating. Each body of water is different and the fish won't eat the same bait; it's really strange. I can throw a Mepps spinner in any lake or river and pull a trout, but it's not the same with carp.
I'm headed over to Tractor Supply for anything fishy, squid, something savory to see if that will improve my non-catch rate. And, I think that carp, like humans, want something that tastes good. I've seen too many carp take in a bait only to spit it out and move on. It's the darndest thing because I think they are a lot smarter than we give them credit for.