diff --git a/specs/transports-v2/http.md b/specs/transports-v2/http.md
index a735f80032..ddba4c9425 100644
--- a/specs/transports-v2/http.md
+++ b/specs/transports-v2/http.md
@@ -11,6 +11,11 @@ The server indicates payment is required using the HTTP 402 "Payment Required" s
 **Mechanism**: HTTP 402 status code with `PAYMENT-REQUIRED` header
 **Data Format**: Base64-encoded `PaymentRequired` schema in header
 
+The `PAYMENT-REQUIRED` header is the canonical HTTP transport location for the
+`PaymentRequired` object. A response body may duplicate the same information
+for humans or backward compatibility, but clients and crawlers must not depend
+on the body alone for x402 protocol data.
+
 **Example:**
 
 ```http
diff --git a/specs/x402-specification-v2.md b/specs/x402-specification-v2.md
index 470bb9a9ca..b3727597a5 100644
--- a/specs/x402-specification-v2.md
+++ b/specs/x402-specification-v2.md
@@ -69,7 +69,9 @@ This section defines the core data structures used in the x402 protocol. These a
 
 **5.1.1 JSON Payload**
 
-When a resource server requires payment, it responds with a payment required signal and a JSON payload containing payment requirements. Example:
+When a resource server requires payment, it responds with a payment required signal containing the `PaymentRequired` object. The transport defines where this object is carried. For HTTP, the canonical wire location is the base64-encoded `PAYMENT-REQUIRED` response header, not only the response body. See [HTTP Payment Required Signaling](./transports-v2/http.md#payment-required-signaling).
+
+Example `PaymentRequired` object:
 
 ```json
 {