diff --git a/packages/shared/src/cbor/AdvertDatum.ts b/packages/shared/src/cbor/AdvertDatum.ts
index 3382290..b71770a 100644
--- a/packages/shared/src/cbor/AdvertDatum.ts
+++ b/packages/shared/src/cbor/AdvertDatum.ts
@@ -118,19 +118,24 @@ export function encodeAdvertDatum(d: AdvertDatum): string {
             throw new Error(`unknown AdvertStatus: ${String(d.status)}`);
           })();
 
+  // cbor-x encodes JS Number as float64 (`fb` prefix) for values that don't
+  // fit in CBOR's compact int forms — and Plutus Data has NO float type, so
+  // CML's PlutusData.from_cbor_hex panics with "RuntimeError: unreachable"
+  // when it sees one. Coerce numeric fields to BigInt so cbor-x always emits
+  // CBOR major-type-0/1 integers. Mirrors the intAsBig pattern in EscrowDatum.
   const cbor = plutusTag(121, [
     hexToBytes(d.supplier_pkh),
     utf8Bytes(d.capability_id),
     utf8Bytes(d.model),
-    d.max_output_tokens,
-    d.max_processing_ms,
+    BigInt(d.max_output_tokens),
+    BigInt(d.max_processing_ms),
     d.price_lovelace,
     d.supplier_bond_lovelace,
     d.buyer_bond_lovelace,
     utf8Bytes(d.endpoint_url),
     utf8Bytes(d.detail_uri),
     hexToBytes(d.detail_hash),
-    d.advertised_at,
+    BigInt(d.advertised_at),
     statusTag,
   ]);
 
diff --git a/packages/shared/src/tx/advert/postAdvert.ts b/packages/shared/src/tx/advert/postAdvert.ts
index df3d32b..61406cf 100644
--- a/packages/shared/src/tx/advert/postAdvert.ts
+++ b/packages/shared/src/tx/advert/postAdvert.ts
@@ -19,6 +19,7 @@ import { loadBlueprint } from "../blueprint.js";
 import { encodeTxBody, sha256Hex } from "../internal/testTxBody.js";
 import { mockSlotToWallclockMs } from "../internal/constants.js";
 import { detectCborBackend } from "../internal/cborBackend.js";
+import type { LiveOgmiosProvider } from "../../chain/LiveOgmiosProvider.js";
 
 const FIVE_MIN_MS = 5 * 60 * 1000;
 
@@ -64,6 +65,19 @@ export async function buildPostAdvertTx(
   }
 
   // 4. Construct tx body.
+  // Live path: route to lucid-evolution so the on-chain submission carries
+  // valid Conway-era CBOR. Mock path keeps the JSON-in-hex synthetic body.
+  if (isLive) {
+    const liveCborPath = "../internal/liveCbor.js";
+    const { buildLiveTxForAdvert } = await import(/* @vite-ignore */ liveCborPath);
+    return buildLiveTxForAdvert({
+      chain: chain as LiveOgmiosProvider,
+      walletKey,
+      advertDatum,
+      deposit_lovelace,
+    });
+  }
+
   const blueprint = loadBlueprint();
   const advertScriptAddress = blueprint.advertScriptAddress(0);
 
diff --git a/packages/shared/src/tx/internal/liveCbor.ts b/packages/shared/src/tx/internal/liveCbor.ts
index 6e3c5ed..3a9f4c4 100644
--- a/packages/shared/src/tx/internal/liveCbor.ts
+++ b/packages/shared/src/tx/internal/liveCbor.ts
@@ -342,8 +342,18 @@ async function buildSpendOpenOrClaimedTx(opts: {
 
     // Let lucid pick coins + compute fee normally; production wallets have
     // multiple real UTxOs (no need for the test-side leftover-as-fee hack).
+    //
+    // localUPLCEval: false — delegate Plutus V3 phase-2 evaluation to Ogmios
+    // (which uses cardano-node's evaluator). lucid 0.4.30's CML WASM UPLC
+    // interpreter has a false-rejection bug for our V3 spend pattern: it
+    // rejects valid txs with "failed script execution Spend[0] the validator
+    // crashed / exited prematurely" while the chain itself accepts them
+    // without complaint. Routing eval to Ogmios sidesteps the WASM bug AND
+    // produces correct ex-units. The provider already implements evaluateTx
+    // (OgmiosLucidProvider.evaluateTx → JSON-RPC evaluateTransaction).
     const completed = await txBuilder.complete({
       presetWalletInputs: realWalletUtxos,
+      localUPLCEval: false,
     });
     signed = await completed.sign.withWallet().complete();
   } catch (err) {