fix(transaction-pay-controller): resolve correct networkClientId for source chain in relay execute

packages/transaction-pay-controller/CHANGELOG.md

@@ -7,6 +7,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Fixed
+
+- Resolve correct `networkClientId` for source chain in Relay execute flow ([#8492](https://github.com/MetaMask/core/pull/8492))
+
 ## [19.2.0]
 
 ### Changed

packages/transaction-pay-controller/src/strategy/relay/relay-submit.test.ts

@@ -1272,6 +1272,7 @@ describe('Relay Submit Utils', () => {
         expect(getDelegationTransactionMock).toHaveBeenCalledWith({
           transaction: expect.objectContaining({
             chainId: CHAIN_ID_MOCK,
+            networkClientId: NETWORK_CLIENT_ID_MOCK,
             nestedTransactions: [
               {
                 data: '0x1234',
@@ -1283,6 +1284,14 @@ describe('Relay Submit Utils', () => {
         });
       });
 
+      it('resolves networkClientId for source chain instead of inheriting from original transaction', async () => {
+        await submitRelayQuotes(request);
+
+        expect(findNetworkClientIdByChainIdMock).toHaveBeenCalledWith(
+          CHAIN_ID_MOCK,
+        );
+      });
+
       it('submits to /execute with delegation data', async () => {
         await submitRelayQuotes(request);
 

packages/transaction-pay-controller/src/strategy/relay/relay-submit.ts

@@ -400,9 +400,15 @@ async function submitViaRelayExecute(
   const { from, sourceChainId } = quote.request;
   const { requestId } = quote.original.steps[0];
 
+  const networkClientId = messenger.call(
+    'NetworkController:findNetworkClientIdByChainId',
+    sourceChainId,
+  );
+
   const sourceCallTransaction = {
     ...transaction,
     chainId: sourceChainId,
+    networkClientId,
     nestedTransactions: allParams.map((params) => ({
       data: (params.data ?? '0x') as Hex,
       to: params.to as Hex,