Are there many other fish in the tank with this copper band? I only started having success with copper band's when I began quarantining them alone in an environment where the foods I was trying to get them to eat were available for hours instead of the minutes they are in a tank with food competition. It takes them a while to figure out they like frozen foods, but if you've got them in a tank with other fish, said foods are rarely around long enough for them to really do much sampling.
I went through 2 Copper bands before trying QTing my third in a tank by itself. It exhibited the same habits as the first two, not really eating anything, but kind of inspecting it, but since it was all alone, the mysis it didn't eat just blew about in the current (it was a tank transfer tank, so it didn't have a filter to suck it up either). It gave it all the time it needed to sample a bit here, sample a bit there, then figure out that it liked it better than being hungry. By the end of the first week, it was actively seeking out the mysis, and none would be left after a few minutes. I also just left a clam on the half shell in the tank the whole time (obviously throwing it out and replacing it at least once a day). It completely ignored it at first, but with no other fish or snails to eat it, and a small enough tank that it couldn't really get away from it, it eventually sampled it.
By the end of the 12 day tank transfer protocol I had a copper band that ate both large and small frozen mysis, frozen brine, clams, and scallop, and aggressively enough to compete with a tank full of fish. I lost him along with all my fish to a temperature spike, and when I replaced him I did the same thing with similar success. The major downside was that both fish went in to my display fully adjusted to a captive diet and had exactly zero interest in aiptasia. Not sure those are related, but if you know you're going to get a delicious clam every morning and a smorgasbord of frozen treats every evening, it probably makes eating aiptasia seem like a dumb waste of stomach space.