diff --git a/docs/INTEGRATION_GUIDE.md b/docs/INTEGRATION_GUIDE.md
index fd78674..f61332c 100644
--- a/docs/INTEGRATION_GUIDE.md
+++ b/docs/INTEGRATION_GUIDE.md
@@ -139,6 +139,7 @@ try {
 - Keep provider URLs in environment variables, not hard-coded.
 - Avoid printing tokens in production pages.
 - Expect `429 Too Many Requests` from provider control endpoints under abuse protection; implement backoff/retry instead of tight loops.
+- If you call provider WebAuthn login challenge/verify endpoints directly, use `POST` only.
 - Rotate client secrets for confidential clients.
 - Add a unique `nonce` to each OIDC authorisation request.
 - Validate `state` on every callback request.