Pro and Max as a monthly subscription, billed by Google Play.
In the Android app, Pro and Max are monthly subscriptions that renew automatically. You pay through Google Play, with the payment methods your Google Play account already uses, so you do not need a separate card for SonnaLabs.
The subscription lives in Google Play: you change or cancel it there, not in SonnaLabs. The credits of an active subscription roll over for as long as the subscription stays active.
Sign in with the same account on the web and on Android and you see one credit balance. Credits bought through Google Play can be used on the web, and credits bought on the web can be used in the Android app.
Pay-as-you-go credit packs are bought on the web, and the web gives more credits for the same price. The Free plan stays free on both: 10,000 credits every month.
Monthly subscription
Google Play
Google Play
Android and the web