diff --git a/contrib/fx/sources.d/80-remote-api.sh b/contrib/fx/sources.d/80-remote-api.sh
index fc44d4d..af8d316 100755
--- a/contrib/fx/sources.d/80-remote-api.sh
+++ b/contrib/fx/sources.d/80-remote-api.sh
@@ -10,6 +10,15 @@
 # assumed, since guessing one could silently pick something you don't
 # want to pay for. Silently no-ops if any of the three is missing.
 #
+# FX_REMOTE_API_URL is the exact URL to POST to -- no "/chat/completions"
+# auto-appended. An earlier version guessed that suffix onto whatever
+# base URL was given, which works for OpenAI/OpenRouter/Groq's actual
+# convention but broke, silently, against a real third-party API that
+# used a different path (a local FastAPI service with a plain "/chat"
+# endpoint, not "/chat/.../completions" -- confirmed live: the guessed
+# URL 404'd, the real one worked). Silent failure on a wrong guess is
+# worse than requiring the full URL up front.
+#
 # Numbered 80: after the free local-LLM source (70) and before
 # 90-team-shared.sh, which is a human-curated source and gets the final
 # word. This is the most expensive tier in latency and real dollar
@@ -63,7 +72,7 @@ payload = {
 }
 
 req = urllib.request.Request(
-    url.rstrip("/") + "/chat/completions" if not url.rstrip("/").endswith("/chat/completions") else url,
+    url,
     data=json.dumps(payload).encode(),
     headers={
         "Content-Type": "application/json",