Update src/pages/learn/debug-errors.mdx

Co-authored-by: Benjie <benjie@jemjie.com>

Author: sarahxsanders

src/pages/learn/debug-errors.mdx

@@ -39,7 +39,7 @@ and may allow `GET` for queries.
 ### Common causes
 
 - Sending a `PUT` or `DELETE` request instead of `POST` or `GET`
-- Sending a `GET` request for a mutation
+- Sending a `GET` request for a mutation, or to a server that only supports `POST` requests
 
 ### How to debug