Is 1,000,000 pub-sub messages monthly? And do you consider each message an API call?

Messaging Service
1

We are implementing a chat app, similar to WahtsApp. There will be one open group/channel/room with 1,000+ people talking in it.
Q1\ Is the 1,000,000 pub/sub messages limitation (on the free tier), monthly?
Q2\ Do you consider each chat pub/sub message (push or pull) an API call?

2 
Q1\ Is the 1,000,000 pub/sub messages limitation (on the free tier), monthly?

Yes

Q2\ Do you consider each chat pub/sub message (push or pull) an API call?

Each publish request is an API call. For the subscribers, each polling request is counted as an API call as well.