purchased app disappeared

I purchased an app (tinycam monitor pro) a few months ago on a Moto X. I recently upgraded my phone to a Samsung S7 edge. When I go to the play store, the app doesn't show up in my apps, and it doesn't show up as purchased either. Searching for the app in the play store gives me the option to purchase it again. But on the old phone, it shows up as installed. I am logged into the same account on both phones. Also checked in browser, and app purchase also doesn't show up. I was under the impression that I could use the app on my new phone without having to purchase it again. Was I wrong?

No, I don't think you understood. The app still runs on the Moto X. It still shows up as installed there. But it doesn't show up as purchased on other devices. (Also, the app is still supported on both Moto X and S7 edge.)

Mystery solved! I had purchased the app via amazon app store, not via google app store. (A little silly that one app store can't detect that an app is already installed on a phone, and label it to indicate that it was installed elsehow.)