Document self-registration toggle

API.md

@@ -162,7 +162,12 @@ X-RateLimit-Reset: 1234567890
 
 **POST** `/api/users/register/` (Public)
 
-Creates new user account and sends verification email.
+Creates a new user account and sends a verification email when self-registration is enabled.
+
+**Availability:**
+- Controlled by `ALLOW_SELF_REGISTRATION`
+- Disabled by default
+- Returns `403 Forbidden` when self-registration is off
 
 **Request:**
 ```json
@@ -1056,7 +1061,7 @@ Use `page` query parameter to navigate: `?page=2`
 
 ### Complete Workflow Example
 
-**1. Register:**
+**1. Register:** `ALLOW_SELF_REGISTRATION=True` only
 ```bash
 POST /api/users/register/
 {
@@ -1067,6 +1072,8 @@ POST /api/users/register/
 }
 ```
 
+**If self-registration is disabled:** create the user through Django admin or another internal provisioning flow, then continue with verification/approval as needed.
+
 **2. Verify Email:**
 ```bash
 POST /api/users/verify-email/