Merge pull request #213354 from ntrogh/alt-vnet-troubleshoot

[Azure Load Testing] Added troubleshooting info for invalid subnet ID

Author: prmerger-automator[bot]

articles/load-testing/how-to-test-private-endpoint.md

@@ -153,14 +153,17 @@ You can specify the VNET configuration settings in the load test creation/update
 
         :::image type="content" source="media/how-to-test-private-endpoint/edit-test.png" alt-text="Screenshot that shows the Tests page, highlighting the button for editing a test.":::
 
-1. Review or fill the load test information. Follow these steps to [create or manage a test](./how-to-create-manage-test.md).
-
 1. On the **Load** tab, select **Private** traffic mode, and then select your virtual network and subnet.
 
     If you have multiple subnets in your virtual network, make sure to select the subnet that will host the injected test engine VMs.
 
     :::image type="content" source="media/how-to-test-private-endpoint/create-new-test-load-vnet.png" alt-text="Screenshot that shows the Load tab for creating or updating a load test.":::
 
+    > [!IMPORTANT]
+    > Make sure you have sufficient permissions for managing virtual networks. You require the [Network Contributor](/azure/role-based-access-control/built-in-roles#network-contributor) role.
+
+1. Review or fill the load test information. Follow these steps to [create or manage a test](./how-to-create-manage-test.md).
+
 1. Select **Review + create** and then **Create** (or **Apply**, when updating an existing test).
 
     When the load test starts, Azure Load Testing injects the test engine VMs in your virtual network and subnet. The test script can now access the privately hosted application endpoint in your VNET.
@@ -196,12 +199,19 @@ To configure the load test with your virtual network settings, update the [YAML
 
     For more information about the YAML configuration, see [test configuration YAML reference](./reference-test-config-yaml.md).
 
+    > [!IMPORTANT]
+    > Make sure you have sufficient permissions for managing virtual networks. You require the [Network Contributor](/azure/role-based-access-control/built-in-roles#network-contributor) role.
+
 1. Save the YAML configuration file, and commit your changes to the source code repository.
 
 1. After the CI/CD workflow triggers, your load test starts, and can now access the privately hosted application endpoint in your VNET.
 
 ## Troubleshooting
 
+### Creating or updating the load test fails with `Subnet ID passed is invalid`
+
+To configure a load test in a virtual network, you must have sufficient permissions for managing virtual networks. You require the [Network Contributor](/azure/role-based-access-control/built-in-roles#network-contributor) role, or a parent of this role, on the virtual network. See [Check access for a user to Azure resources](/azure/role-based-access-control/check-access) to verify your permissions.
+
 ### Starting the load test fails with `Test cannot be started`
 
 To start a load test, you must have sufficient permissions to deploy Azure Load Testing to the virtual network. You require the [Network Contributor](/azure/role-based-access-control/built-in-roles#network-contributor) role, or a parent of this role, on the virtual network. See [Check access for a user to Azure resources](/azure/role-based-access-control/check-access) to verify your permissions.