Cassy plans are paid from your Wiply wallet, so you need enough credit in it first.

1. On wiply.net, top up your wallet if needed.
2. In Cassy, open the account menu → Plans.
3. Choose Monthly or Yearly, then Get Plus or Get Pro.
4. A wiply.net page shows the plan, the price and your wallet balance. Check them and click Pay.
5. You are taken back to Cassy. Your plan starts within a minute, with a full day of credits.

If your wallet doesn't have enough credit, the payment page tells you and links to the wallet: top it up and open the page again.