[Billing] Add threshold billing documentation (#29895)

* [Billing] Add threshold billing documentation

Add new page documenting the threshold billing feature for usage-based products.
Covers how threshold billing works, affected products, payment failure handling,
and FAQ.

* Update src/content/docs/billing/threshold-billing.mdx

Co-authored-by: marciocloudflare <83226960+marciocloudflare@users.noreply.github.com>

* Update src/content/docs/billing/threshold-billing.mdx

Co-authored-by: marciocloudflare <83226960+marciocloudflare@users.noreply.github.com>

* Update src/content/docs/billing/threshold-billing.mdx

Co-authored-by: marciocloudflare <83226960+marciocloudflare@users.noreply.github.com>

---------

Co-authored-by: marciocloudflare <83226960+marciocloudflare@users.noreply.github.com>

Author: tpikovskaia

src/content/docs/billing/threshold-billing.mdx

@@ -0,0 +1,105 @@
+---
+title: Threshold billing
+pcx_content_type: concept
+sidebar:
+  order: 11
+  description: Automatic mid-cycle invoicing for usage-based products
+---
+
+import { DashButton } from "~/components";
+
+Threshold billing is an automatic payment collection mechanism for Cloudflare's usage-based products. When your accumulated usage charges reach a certain level during a billing cycle, Cloudflare generates a mid-cycle invoice and charges your payment method on file.
+
+## How threshold billing works
+
+1. **Usage accumulates** - As you use Cloudflare's usage-based products, charges accrue throughout your billing cycle.
+2. **Threshold reached** - When your accumulated usage charges reach the threshold, Cloudflare automatically generates a mid-cycle invoice.
+3. **Payment collected** - Your payment method on file is charged for the threshold invoice amount.
+4. **One-time trigger** - The threshold fires once per subscription. After a threshold invoice is generated, your subscription returns to standard end-of-cycle billing.
+5. **End-of-cycle invoice** - At the end of your billing cycle, you receive your regular invoice which includes only the remaining usage charges not already covered by the threshold invoice.
+
+:::note
+You will never be double-charged. The threshold invoice and end-of-cycle invoice together equal your total usage for the billing period.
+:::
+
+### Example
+
+| Event | Charge |
+| --- | --- |
+| Usage reaches threshold mid-cycle | Threshold invoice charged (for example, $127.50) |
+| End of billing cycle (total usage was $180) | End-of-cycle invoice charged (for example, $52.50) |
+| **Total charged** | **$180** |
+
+## Products subject to threshold billing
+
+Threshold billing applies to the following usage-based products:
+
+- [R2](/r2/)
+- [Stream](/stream/)
+- [Cloudflare Images](/images/)
+- [Workers](/workers/) (usage-based pricing)
+
+## Who is affected
+
+Threshold billing applies to self-serve accounts using the products listed above.
+## Affected accounts
+:::note
+Enterprise accounts and startup program participants are not subject to threshold billing.
+:::
+
+## Multiple subscriptions
+
+If you have multiple usage-based subscriptions (for example, both R2 and Workers on separate subscriptions), the threshold applies to each subscription independently. You may receive one threshold invoice per subscription if each reaches the threshold.
+
+## What happens if payment fails
+
+If the payment for a threshold invoice fails:
+
+1. **Automatic retries** - Cloudflare will automatically retry the payment over a 5-day period.
+2. **Email notification** - You will receive an email notifying you of the failed payment with a link to pay the invoice or update your payment method.
+3. **Manual payment** - You can pay the invoice directly at any time during the retry period through your Cloudflare dashboard.
+
+   <DashButton url="/?to=/:account/billing" />
+
+4. **After retries exhausted** - If all payment retries fail, the invoice is marked as uncollectable and your account may be restricted.
+
+To avoid service interruption, ensure your payment method on file is current and has sufficient funds.
+
+## Viewing your invoices
+
+All threshold invoices appear in your billing history alongside your regular invoices.
+
+1. Log in to the [Cloudflare dashboard](https://dash.cloudflare.com/).
+2. Go to **Manage Account** > **Billing**.
+
+   <DashButton url="/?to=/:account/billing" />
+
+3. Select **Invoices** to view your invoice history.
+
+Threshold invoices are labeled to distinguish them from regular end-of-cycle invoices.
+
+## FAQ
+
+### Why did I receive a mid-cycle charge?
+
+Your usage-based charges reached the billing threshold before the end of your billing cycle. This is expected behavior for accounts with high usage of R2, Stream, Images, or Workers.
+
+### Will I be charged twice for the same usage?
+
+No. The threshold invoice covers usage up to the point when the threshold was reached. Your end-of-cycle invoice includes only the remaining usage after that point. The two invoices together equal your total usage for the billing period.
+
+### Can I change the threshold amount?
+
+The threshold is automatically set by Cloudflare and cannot be modified.
+
+### Will I get another threshold invoice next month?
+
+No. The threshold fires once per subscription. After the first threshold invoice, your subscription returns to standard end-of-cycle billing for all future cycles.
+
+### How do I avoid threshold invoices?
+
+Threshold invoices are triggered by usage. If you prefer not to receive mid-cycle invoices, you can monitor your usage and adjust your product consumption accordingly. However, threshold billing is designed to help you pay as you go rather than receiving a large bill at the end of the month.
+
+### What if I think I was charged incorrectly?
+
+If you believe there is an error with your threshold invoice, [contact Cloudflare support](/support/contacting-cloudflare-support/) with your invoice details.