feat: add doc for seat limit based plans for Clerk Billing (#3266)

Author: l-armstrong

docs/guides/billing/seat-limit-plans.mdx

@@ -0,0 +1,50 @@
+---
+title: Plans with seat limits
+description: Restrict organization membership by Plan tier using seat-based limits
+---
+
+<Include src="_partials/billing/billing-experimental" />
+
+Membership limits on organizations can now be granted directly by subscribing to a Clerk Billing Plan, allowing organizations to purchase a higher membership limit in a self-serve fashion.
+This makes it possible to target Plans to organizations based on their specific size. For example, you may let organizations use your most affordable Plan for up to ten seats, but require them to upgrade to a more expensive Plan to get unlimited seats.
+
+## Creating a Plan with a seat limit
+
+To create a Plan with a seat limit:
+
+1. Navigate to the [**New Organization plan**](https://dashboard.clerk.com/~/billing/plans/new/org) page in the Clerk Dashboard.
+1. Toggle on the **Seat-based** section.
+1. If you'd like to set a limit, select **Custom limit** and enter the desired value. (You need the B2B Authentication add-on to set a limit greater than 20.)
+1. If you'd like the Plan to allow an unlimited number of seats, select **Unlimited members**. (You need to have the B2B Authentication add-on to select this option.)
+
+> [!IMPORTANT]
+>
+> - Plans created with seat limits cannot have the seat limit removed or changed. Similarly, Plans created without seat limits cannot have seat limits added after the Plan is created.
+> - Organizations subscribed to Plans with seat limits on them will have their membership limit set to the Plan's seat limit.
+> - Organizations subscribed to Plans without seat limits will have their membership limit set to the [default membership limit](/docs/guides/organizations/configure#membership-limits). This can be overridden on a per-organization basis.
+> - If an organization's seat limits are forcibly lowered (e.g., their subscription ending or their Plan being changed by an administrator), the organization will keep their currently provisioned seats but cannot invite new members until they're under the new seat limit.
+> - When an organization is on a seat-limited Plan, you cannot manually set the organization's seat limit.
+
+## SDK version requirements
+
+To use seat limits, you need to be using the following Clerk SDK versions:
+
+- `@clerk/react` v6.1.4 or higher
+- `@clerk/nextjs` v7.0.8 or higher
+- `@clerk/expo` v3.1.6 or higher
+- `@clerk/react-router` v3.0.8 or higher
+- `@clerk/tanstack-react-start` v1.0.8 or higher
+
+## Managing seat limits
+
+### Organization invitations
+
+When an organization subscribes to a Plan with seat limits, they'll be able to invite members to their organization up to the Plan's limit, as well as revoke invitations that were already sent out.
+
+Once an organization reaches the seat limit, they will no longer be able to invite new members.
+
+### Changing Plans
+
+If an organization wants to switch to a Plan with a seat limit and the organization has more members than allowed by the Plan, they must remove members from their organization prior to switching Plans.
+
+If an organization wants to switch from a seat-limited Plan to a Plan without seat limits and is currently over the default membership limit for organizations, they must remove members before switching Plans.

docs/manifest.json

@@ -564,6 +564,10 @@
                     "title": "Free trials",
                     "href": "/docs/guides/billing/free-trials"
                   },
+                  {
+                    "title": "Plans with seat limits",
+                    "href": "/docs/guides/billing/seat-limit-plans"
+                  },
                   {
                     "title": "Default Plans",
                     "href": "/docs/guides/billing/default-plans"