Ruby Amulet doesn't seem to be able to accepts any charms.

I have a similar problem. I can add 2 charms to a Gold Necklace [0/2] (didn't realize that only 1 of the charms on the coin passed over but it's a learning process). I can't seem to add any charms to a Ruby Amulet [0/4].

Could not reproduce. Did not receive reply from poster (curseforge comments).