I am in a weird situation with a few friends that we made an appointment scheduling application for a client who tried several others and found nothing they lik

I am in a weird situation with a few friends that we made an appointment scheduling application for a client who tried several others and found nothing they liked and kept reverting to using google calendar. Now we built them this perfect app that they love, but we can't seem to sell it to anyone else. It's looking more and more like we spent six months developing an app for essentially one client (technically we have three, one client has two shops, and one employee that left started his own and uses it).