diff --git a/README.md b/README.md
index e9da455..6af0772 100644
--- a/README.md
+++ b/README.md
@@ -134,6 +134,7 @@ This wrapper now delegates to `BlackWall\Auth\AuthClient`.
 - Use OAuth/portal authentication endpoints for end users; provider admin login endpoints enforce separate admin scope checks.
 - Never place client secrets, refresh tokens, or access tokens in URL query strings.
 - For OIDC providers, include a per-request `nonce` in authorisation requests.
+- For direct Cryptbin API usage, send `key_b64url` on unwrap calls; provider rejects key-mismatch unwrap attempts with `403 Forbidden`.
 - Always use HTTPS in production.
 - Store refresh tokens securely.
 - Keep access tokens out of logs and browser-visible output.
diff --git a/docs/INTEGRATION_GUIDE.md b/docs/INTEGRATION_GUIDE.md
index 6c163fa..ff6acba 100644
--- a/docs/INTEGRATION_GUIDE.md
+++ b/docs/INTEGRATION_GUIDE.md
@@ -162,3 +162,4 @@ Provider user/project assignment views may exclude disabled projects even if his
 - Use secure session cookies (`Secure`, `HttpOnly`, `SameSite=Lax` or stricter).
 - HTTPS URLs are enforced by default in `Config::fromArray()`.
 - For localhost-only HTTP testing, explicitly set `allowInsecureHttp => true`.
+- If you call Cryptbin unwrap APIs directly, include the original share key as `key_b64url`; unwrap now returns `403 Forbidden` when key proof does not match metadata verifier.