diff --git a/web/src/app/v1/consumption/daily/route.ts b/web/src/app/v1/consumption/daily/route.ts
index a42f94a..896b232 100644
--- a/web/src/app/v1/consumption/daily/route.ts
+++ b/web/src/app/v1/consumption/daily/route.ts
@@ -7,13 +7,13 @@ export const runtime = "nodejs";
 export const dynamic = "force-dynamic";
 
 /**
- * Upsert on (installationId, date), incrementally. The car sends a 30-minute delta chunk
+ * Upsert on (installationId, date), incrementally. The car sends a 2-minute delta chunk
  * (not a cumulative total), so each PUT adds to the day's running totals rather than
  * overwriting them. Lifetime is a snapshot — the latest one wins, so it is $set not $inc.
  *
- * The old cumulative-overwrite format still works: a record whose day totals already
- * represent the full day simply adds them again, which is wrong — but the app no longer
- * sends that format, and the legacy 189 km document is never re-sent. New data only.
+ * $setOnInsert seeds the whole `day` subdocument as a nested object (not dotted paths)
+ * because $inc and $setOnInsert cannot touch the same field — MongoDB rejects that with
+ * a 500, which is what held the 20 cached chunks back.
  */
 export async function PUT(request: Request) {
   const denied = requireIngest(request);
@@ -23,27 +23,26 @@ export async function PUT(request: Request) {
     await ensureIndexes();
     const collection = await consumptionCollection();
     const updatedAt = new Date();
-    const setOnInsert: Record<string, unknown> = {
-      createdAt: updatedAt,
-      installationId: record.installationId,
-      date: record.date,
-      "day.km": 0, "day.kwh": 0, "day.hours": 0, "day.socDrop": 0,
-    };
-    const update: Record<string, Record<string, unknown>> = {
-      $inc: {
-        "day.km": record.day.km,
-        "day.kwh": record.day.kwh,
-        "day.hours": record.day.hours,
-        "day.socDrop": record.day.socDrop,
-      },
-      $set: { updatedAt },
-      $setOnInsert: setOnInsert,
-    };
-    if (record.lifetime) update.$set.lifetime = record.lifetime;
-    if (record.sohPercent !== undefined) update.$set.sohPercent = record.sohPercent;
+    const $set: Record<string, unknown> = { updatedAt };
+    if (record.lifetime) $set.lifetime = record.lifetime;
+    if (record.sohPercent !== undefined) $set.sohPercent = record.sohPercent;
     await collection.updateOne(
       { installationId: record.installationId, date: record.date },
-      update,
+      {
+        $inc: {
+          "day.km": record.day.km,
+          "day.kwh": record.day.kwh,
+          "day.hours": record.day.hours,
+          "day.socDrop": record.day.socDrop,
+        },
+        $set,
+        $setOnInsert: {
+          createdAt: updatedAt,
+          installationId: record.installationId,
+          date: record.date,
+          day: { km: 0, kwh: 0, hours: 0, socDrop: 0 },
+        },
+      },
       { upsert: true },
     );
     return new NextResponse(null, { status: 204 });