Credit

Every S2 Module has a SIM and a data plan built in. You pay for the data that your code and your application send, with credit that you add to a fleet in advance. There is no subscription or contract.

Prices
What spends credit
When a fleet runs out of credit
Check the balance
Top up a fleet
Credit belongs to a fleet

Prices

Item	Price
Starter credit	€10, included with every new S2
Data	€1 per MB, where 1 MB is 1,000,000 bytes
Top-up	From €1 to €1,000 at a time, before tax

The price covers the network overhead around your data. Superstack counts only your data and a few bytes that label it, such as the field names around each log, so you can estimate the cost from the size of your own data:

cost per day = bytes per day / 1,000,000 × €1

Code that sends 200 bytes a minute sends 288,000 bytes a day, which costs about €0.29 a day.

What spends credit

These spend credit, in both directions:

Code uploads. An upload sends each device only the files that differ from the ones it holds. A fleet upload sends them to every device in the fleet.
Logs. The output of print(), and the logs that say code started, ended, stopped or crashed.
Messages to a device, from your application or from another device’s Lua.
Web requests from Lua. A request counts its URL, headers and body, and the response counts its status and body, or its error.

Data that the network resends on its own spends nothing, and a device that is offline spends nothing. An upload or a message that fails partway, such as over a weak connection, spends credit for the part that arrived, and each retry spends again.

These are free:

Check-ins between the S2 and Superstack.
Pairing and unpairing.
Starting, stopping and restarting code.
Firmware updates.

When a fleet runs out of credit

A fleet has no credit when its balance is zero or less. Its code keeps running, but no data that spends credit leaves the S2 or Superstack:

Superstack refuses uploads to the fleet. superstack upload says that the fleet has no credit.
Superstack refuses messages to the fleet with 402 Payment Required.
The S2 discards its logs instead of sending them.
A web request from Lua returns the error no credit straight away.
Superstack holds the messages already queued for the fleet, and delivers them after a top-up unless they expire first.
superstack device list shows no credit for a device whose code is waiting to be sent.

You can still pair and unpair the S2, and start, stop and restart its code. The S2 still installs firmware updates.

Data already on its way when the credit runs out is still charged, whether Superstack delivers it or refuses it, so the balance can go below zero. The next top-up pays that first.

Check the balance

superstack account balance

The CLI lists each fleet you can reach with its balance:

ID  NAME            BALANCE
12  My first fleet  €9.71

Add a fleet id to show one fleet. The owner and every member of a fleet can see its balance and top it up.

Top up a fleet

Run:
```
 superstack account topup <fleet_id>
```

The CLI prints the address of the payment page:

 Open this page to choose an amount and pay:

   https://checkout.stripe.com/c/pay/...

 The credit appears on the balance once the top-up completes.
 Press enter to open the browser.

Press Enter. Your browser opens the payment page. You can also open the address in any browser, such as on your phone.
Choose an amount, and pay.

The credit shows in superstack account balance once the payment completes. Superstack tells each S2 in the fleet straight away, and it starts sending data again. An S2 in low power mode waits for its next check-in.

Credit belongs to a fleet

Credit belongs to a fleet, never to a device:

A new S2 gives its starter credit to the first fleet it is paired with, and that fleet keeps it.
Unpairing an S2, or giving it to someone else, moves no credit.
A second-hand S2 brings no starter credit. Top up its new fleet before you upload code to it.
Transferring a fleet to a new owner moves its credit with it.
Deleting a fleet forfeits its remaining credit.

Swedish bookkeeping law requires Silicon Witchery to keep each fleet’s record of top-ups and spending, so the record stays after you delete the fleet or your account. It names the fleet, not you.