What if a customer app did not get approved?

Maybe this is not the right place to ask, but im trying
i have a small agency that almost do everything digital (from sites, custom software and so), until today we declined request on making app, but now i sarted to get into expo and i found that a lot of app we were requested to implement (mainly app interfaces to existing website, with some functionality that can be useful onf mobile device) can be perfectly done in react native and expo. We developed some piece of code to showcase our customer what the app is capable to do (things like logins, getting data from remote, saving to favorites, preferences, map and location and so on), all inside Expo. At the moment we have no experience on building an app (that shouldn’t be a big deal) and submitting to stores, which is the part that concern us… what happen if a customer app did not get approved? how we manage it? how may “fixes” we should support? and what if the app concept is not accepted? can we be responsible for not having take that in context?

thanks to everyone sharing his experience