diff --git a/docs/specification/shopping/checkout/rest.md b/docs/specification/shopping/checkout/rest.md
index 1faa4e40f..1c0db05a5 100644
--- a/docs/specification/shopping/checkout/rest.md
+++ b/docs/specification/shopping/checkout/rest.md
@@ -1437,7 +1437,7 @@ Content-Type: application/json
 UCP-Agent: profile="https://platform.example/.well-known/ucp"
 Idempotency-Key: 550e8400-e29b-41d4-a716-446655440000
 Content-Digest: sha-256=:X48E9q...:
-Signature-Input: sig1=("@method" "@authority" "@path" "idempotency-key" "content-digest" "content-type");keyid="platform-2025"
+Signature-Input: sig1=("@method" "@authority" "@path" "ucp-agent" "idempotency-key" "content-digest" "content-type");keyid="platform-2025"
 Signature: sig1=:6G4i8TS6oUkGrx8KnCFUpsSPwd74...:
 
 {"line_items":[{"item":{"id":"item_123"},"quantity":2}]}