1. Login to Fluss Admin Dashboard: Visit https://fluss.io/ and login.
2. Once logged in, locate and click on the "Flusses" section.
3. Click on "Manage" next to the device you want to updrade.
4. Locate and click on the "Billing" section.
5. Click on "Accounts"
6. Click on "Default" block, then edit account and "Add Payment Method"
NB: There's only one Payment Method, which is card payment.