As you have started the sentence talking about one single app, "latter" wouldn't be suitable nor clear to be used for referring to drivers. However, it is possible to use it if you restructured your sentence like this for example:
It was planned to make an app for users to find drivers, and
another app for drivers to serve the users. The former has been
implemented while the latter hasn't been.
I have shown this to a native English speaker, he said that "latter" can refer to "drivers", but it would be poorly worded; otherwise, "latter" would refer to the whole meaning of the sentence which is allowing users to find drivers.
He responded after you have provided the previous context that it is still ambiguous, so he recommends you change it to be more explicit:
- For real-world scenarios, where maximum
clarity is important, you can state:
There was no app for drivers to find users.
- However, if the goal of the writing is to sound impressive by using fancy vocabulary, then you could say:
There was no app for vice versa.
- Alternatively, if you just want to be clear without using posh words and without mentioning Drivers or Users again explicitly, you could then write:
There was no app for the other way round.
which is also very clear but just sounds a bit basic.