KarMar has it right. If you are using bells, you HAVE to let them out EVERY SINGLE TIME they ask. For a while, they will drive you crazy, and ask much more often than they really need to go, but eventually the novelty will wear off when they realize there's not much reward for just asking to go out when they don't need to potty.
It's the one disadvantage of the system. (Besides the fact that the bells don't ALWAYS translate to a new location, like a vacation house or a hotel room) But the advantage of having a dog who can consistently ASK to go out is big enough that most people are willing to live though the annoying phase.
I didn't use bells with my older two. Kodi found them aversive, and wouldn't touch them. He eventually learned, all on his own, to ask with a very distinctive, single bark. Pixel was SO good about using her litter box from the very beginning that there was no real need to establish an "out" signal. She still doesn't have one. She just goes out when the other ones do, or uses the litter box on her own.
I'm considering putting the bells back up for Panda. After her UTI's she decided that the litter boxes were responsible for her discomfort, and she won't use them to pee on, although she will poop there if she needs to. So we've had to just make sure we took her out often enough that she didn't have accidents. She is starting to signal she needs to go out, but but running frantically back and forth by the door, which I can't see if I'm not with her. I think she may take to using the bells as a way to let us know when she needs to go out. BUT, she also LOVES to be outside playing, so I foresee a LOT of door opening needs if I go that route.