firebase-admin-node | Firebase Admin Node.js SDK | Authentication library

First, to answer the question @firebase/app is a module that is part of the Firebase Web SDK (you get it by npm install firebase) and never needs to be manually installed, and should not be installed at all for firebase-admin.

So in a nutshell, here is what's going on with this error, in general: firebase-admin has a dependency called @firebase/database, which is shared with the Firebase Web SDK. A recent release of @firebase/database had some changes that caused it to not work if used with an older version of @firebase/app.

So basically, it should work if you have either (1) no @firebase/app or (2) a current @firebase/app. Your error sounds most likely to be an existing outdated @firebase/app.

I know you said you don't seem to have @firebase/app in your project but since it seems like the most likely cause, I'm wondering if you have it in a parent directory. (It's installed as part of the Firebase Web SDK, as in npm install firebase.) Most firebase functions (if you use firebase init) are set up in a /functions subdirectory of the main project repo, with its own package.json, and the rest of the project is one level up and has another package.json. And that looks like it might be your dir structure?

In that case, running npm ls inside /functions will turn up an empty result, but if you go up to the parent dir (that contains the other package.json), it will show up. Node will go up a level if it doesn't find a package at the current one. See if you can ensure both levels are clean from any @firebase/app, delete both node_modules dirs, reinstall. If you do need it in the top level (for Firebase Web SDK), make sure it is upgraded the most current firebase (7.6.1).

As a last resort, maybe check to see if firebase is npm installed globally somehow.

If you definitely don't have @firebase/app at any level of your project and it's still failing, this is a bug we should look into.

Sorry that's a lot of info! Hope that wasn't too much. TLDR: I think you do probably have @firebase/app in your project root dir? If not, please file an issue on Github.