Document Auto Top-Up

fern/products/platform/pages/platform/core/rate-limits.mdx

@@ -105,6 +105,7 @@ Please be prepared to share detailed information about your use case.
 If approved, you **MUST** set up auto top up on your project to the total cost of the numbers monthly **before the limit will be raised**.
 This requirement prevents the suspension of services due to insufficient balance.
 Pricing for phone numbers can be found on the [SignalWire pricing page](https://signalwire.com/pricing/messaging).
+See [Auto Top-Up](/docs/platform/auto-top-up) for how it is charged and what enabling it commits you to.
 </Warning>
 
 

fern/products/platform/pages/platform/setup/auto-top-up.mdx

@@ -0,0 +1,64 @@
+---
+title: Auto Top-Up
+subtitle: Keep your balance funded automatically, and what enabling it commits you to.
+description: How Auto Top-Up funds your SignalWire balance, when your card is charged, and why it cannot be switched off once it is on.
+slug: /auto-top-up
+max-toc-depth: 3
+---
+
+Adding a payment method to your Space turns on Auto Top-Up.
+When your balance falls below a threshold you set, SignalWire charges the card you chose and adds the funds to your balance.
+This keeps calls and messages running, and keeps recurring charges such as phone numbers paid.
+
+<Warning title="Auto Top-Up cannot be turned off">
+You can change the amount, the threshold, and the card that funds it, but the Dashboard does not offer a way to switch Auto Top-Up off once it is on.
+To turn it off, contact [Support](https://support.signalwire.com/portal).
+</Warning>
+
+## When you are charged
+
+| Setting | Default | Limits |
+| :-- | :-- | :-- |
+| Threshold | `$5` | Minimum `$5`, maximum `$1,000,000` |
+| Top-up amount | `$10` | Minimum `$10` |
+
+The charge is normally the top-up amount.
+If topping up by that amount would still leave your balance at or below the threshold, SignalWire charges enough to clear the threshold and add the top-up amount on top.
+The amount charged can therefore be larger than the amount you configured.
+
+With a threshold of `$50` and a top-up amount of `$10`, a balance that falls to `$5` is charged `$55`.
+
+Auto Top-Up charges at most once every six hours.
+A Space that spends faster than that can reach a zero balance between charges and lose service until the next one, so set a top-up amount that covers six hours of your own traffic.
+
+Some features require Auto Top-Up to be active before you can use them.
+Registering a campaign with [The Campaign Registry](/docs/platform/messaging/campaign-registry) is one of them, and returns the `auto_top_up_deactivated` error while Auto Top-Up is off.
+
+## Change your settings
+
+Open **Billing → Low Balance Settings** in the Dashboard to change the top-up amount, the threshold, and which card funds Auto Top-Up.
+
+## Remove the card that funds Auto Top-Up
+
+A card cannot be removed while it is your Auto Top-Up payment method. To remove it:
+
+<Steps>
+
+### Add another card
+
+Add the replacement payment method to your Space.
+
+### Point Auto Top-Up at the new card
+
+In Low Balance Settings, select the new card as your Auto Top-Up payment method and save.
+
+### Remove the original card
+
+The original card can now be removed from the Payment Methods page.
+
+</Steps>
+
+## If a charge fails
+
+If the charge is declined, or no valid card is on file to charge, SignalWire turns Auto Top-Up off and emails your Space administrators.
+Adding a payment method or topping up your balance manually turns it back on.

fern/products/platform/pages/platform/setup/trial-mode.mdx

@@ -7,6 +7,11 @@ slug: trial-mode
 All new SignalWire accounts begin in Trial Mode, a restricted status to prevent abuse of services.
 To remove Trial Mode, simply add a credit card to your account and fund it with at least $5 of credit.
 
+<Info>
+Adding a payment method also turns on [Auto Top-Up](/docs/platform/auto-top-up),
+which keeps your balance funded automatically and cannot be turned off once it is on.
+</Info>
+
 <CardGroup>
 <Card
     title="Fund your account"