diff --git a/docs/WORK_CYCLE.md b/docs/WORK_CYCLE.md
index f5231a9..bc0164c 100644
--- a/docs/WORK_CYCLE.md
+++ b/docs/WORK_CYCLE.md
@@ -245,11 +245,21 @@ curl -sk -X PATCH -H "$AUTH" -H "Content-Type: application/json" \
 
 **A check-in** — a timestamped "what changed", when there is something real to
 report. `summary` is required and must say something; the API refuses an empty
-"no change" update, deliberately:
+"no change" update, deliberately.
+
+**`projectId` here is the project's UUID, not its slug** — unlike every other
+route on this API, which takes the slug in the path. A slug is rejected with
+`{"error":{"code":"unknown","message":"Something went wrong."}}`, which says
+nothing about which field was wrong and looks exactly like an outage. Read the
+`id` off the project first. There is also **no route that amends a check-in**
+once posted, so get the body right before sending it:
 
 ```bash
+PID=$(curl -sk -H "$AUTH" "$BASE/agent/projects/<slug>" \
+        | python3 -c "import json,sys; print(json.load(sys.stdin)['project']['id'])")
+
 curl -sk -X POST -H "$AUTH" -H "Content-Type: application/json" \
-  -d '{"projectId":"<slug>","health":"on_track",
+  -d '{"projectId":"'"$PID"'","health":"on_track",
        "summary":"<what changed>","accomplishments":"<what landed>",
        "blockers":"<what is stuck, or omit>","nextActions":"<what is next>"}' \
   "$BASE/agent/updates"