Masters of the Air is released on a weekly basis, with ep. 4 coming next Friday. There isn’t more to watch yet. Not sure where you saw the 2.99 for, as Masters of the Air is exclusively on Apple TV+, which has a different subscription price in any dollar country, I think.
1923 is on Paramount+, not Apple TV+. If you want to watch this, you may need to have an active subscription to Paramount+. Note that subscriptions to Paramount+ come in different types that are generally not exchangeable. If you subscribed in the Apple TV app to this, then that is where you should watch it. If you subscribed in the separate Paramount+ app on an Apple device to this, then that is where you should watch it (not the Apple TV app). If you subscribed to this with Paramount+ directly, then you should use the Paramount+ app (not the Apple TV app), and sign in there with your Paramount+ account.
1923 is also available as an iTunes Store TV show to buy in the Apple TV app (no subscription), in the US, CA, UK, DE, FR, AU. Perhaps you saw that as a possible charge option at USD 2.99 per episode or USD 19.99 per season?