In a monorepo on Vercel, how does one app know about the other?

[stephenlindauer]

Summary

Simplified scenario:
In my mono repo, I have a www app and an api app. The www app is the frontend for our website while the api app is just an API that the www app communicates with. (We also have a mobile app and other frontend apps that hit the API, for context.)

Problem:
When building the apps, I want the preview of www to point to the preview of api so I can test my changes in both apps together.

Is it possible to inform the www app about the api app's url during the build? Right now I have them as 2 separate projects in Vercel.

Additional information

No response

Example

No response