diff --git a/mintlify/openapi.yaml b/mintlify/openapi.yaml
index 43321c8af..7944d6f18 100644
--- a/mintlify/openapi.yaml
+++ b/mintlify/openapi.yaml
@@ -5574,6 +5574,9 @@ paths:
       description: |
         Simulate receiving funds into an internal account in the sandbox environment. This is useful for testing scenarios where you need to add funds to a customer's or platform's internal account without going through a real bank transfer or following payment instructions.
         This endpoint is only for the sandbox environment and will fail for production platforms/keys.
+        ### Funding a rule-based account
+        Funding a `RULE_BASED` account triggers its sweep, exactly as a settled deposit does in production: the balance is swept to the rule's destination and the account is left at zero. A balance outside the corridor band moves to the account holder's own account in the same currency instead, and the transaction fails with `failureReason: SWEEP_AMOUNT_OUT_OF_RANGE` — fund a rule-based account with a very small amount to rehearse that path. Either way the rule-based account is left at zero; it never holds a balance.
+        Sandbox simulates the API contract and the routing decision, not the banking rails. The quote, the corridor bounds, the destination checks and the webhook are all real; the settlement legs behind them are not, so timings and failure modes that originate at a partner bank cannot be reproduced here.
       operationId: sandboxFundInternalAccount
       tags:
         - Sandbox
diff --git a/openapi.yaml b/openapi.yaml
index 43321c8af..7944d6f18 100644
--- a/openapi.yaml
+++ b/openapi.yaml
@@ -5574,6 +5574,9 @@ paths:
       description: |
         Simulate receiving funds into an internal account in the sandbox environment. This is useful for testing scenarios where you need to add funds to a customer's or platform's internal account without going through a real bank transfer or following payment instructions.
         This endpoint is only for the sandbox environment and will fail for production platforms/keys.
+        ### Funding a rule-based account
+        Funding a `RULE_BASED` account triggers its sweep, exactly as a settled deposit does in production: the balance is swept to the rule's destination and the account is left at zero. A balance outside the corridor band moves to the account holder's own account in the same currency instead, and the transaction fails with `failureReason: SWEEP_AMOUNT_OUT_OF_RANGE` — fund a rule-based account with a very small amount to rehearse that path. Either way the rule-based account is left at zero; it never holds a balance.
+        Sandbox simulates the API contract and the routing decision, not the banking rails. The quote, the corridor bounds, the destination checks and the webhook are all real; the settlement legs behind them are not, so timings and failure modes that originate at a partner bank cannot be reproduced here.
       operationId: sandboxFundInternalAccount
       tags:
         - Sandbox
diff --git a/openapi/paths/sandbox/sandbox_internal_accounts_{accountId}_fund.yaml b/openapi/paths/sandbox/sandbox_internal_accounts_{accountId}_fund.yaml
index a25767b17..0cfc9b9a0 100644
--- a/openapi/paths/sandbox/sandbox_internal_accounts_{accountId}_fund.yaml
+++ b/openapi/paths/sandbox/sandbox_internal_accounts_{accountId}_fund.yaml
@@ -8,6 +8,23 @@ post:
 
     This endpoint is only for the sandbox environment and will fail for
     production platforms/keys.
+
+    ### Funding a rule-based account
+
+    Funding a `RULE_BASED` account triggers its sweep, exactly as a settled
+    deposit does in production: the balance is swept to the rule's
+    destination and the account is left at zero. A balance outside the corridor
+    band moves to the account holder's own account in the same currency
+    instead, and the transaction fails with
+    `failureReason: SWEEP_AMOUNT_OUT_OF_RANGE` — fund a rule-based account with
+    a very small amount to rehearse that path. Either way the rule-based account
+    is left at zero; it never holds a balance.
+
+    Sandbox simulates the API contract and the routing decision, not the
+    banking rails. The quote, the corridor bounds, the destination checks and
+    the webhook are all real; the settlement legs behind them are not, so
+    timings and failure modes that originate at a partner bank cannot be
+    reproduced here.
   operationId: sandboxFundInternalAccount
   tags:
     - Sandbox