The main page of this APK update states that "PSIPHON 3 UNLIMITED" costs $19.95/yr and has a free seven-day trial. I just tested it out and found that the app can connect without any issues. You still get ads, but at least you will be able to use the VPN service until your seven days is up to decide whether or not you want to buy a subscription for it.
There are some issues with this subscription model. After your week or day trial ends, you are no longer able to connect to servers. And it also appears that you cannot buy coins until your trial runs out either, so please be aware of that if you're thinking about purchasing a subscription for this app! The old model was much better, in my opinion, since at least then I could use it without being forced into buying something first before using the service. I have also had problems on Android 8 where even though I have reinstalled the app, it still tries to force me into buying something every time I open it, so I'm unable to use it on my device, which is sad.
There's a workaround you can use, uninstall Psiphon 3 and reinstall an older version like v3.2 or v3.5 (I currently use v3.7). That way, you won't be forced into buying something first and will still get to use your paid subscription until the day/week trial runs out! The only downside is that there are probably fewer servers available now, so you may have to wait longer before being assigned a server address.