VPC Network error when configuring App Engine for Google Tag Manager Server Side

I'm trying to set up ServerSide Google Tag Manager, which is a service that runs on GCP App Engine.

The setup is done with a few Cloud Shell commands, which are describede here: https://developers.google.com/tag-platform/tag-manager/server-side/script-user-guide#create_a_tagging_server_or_reconfigure_an_existing_tagging_server

However, when I did it originally (even as GCP project owner), I got this error:

I was advised that, to solve this, I needed to manually create a VPC Network called default. So I did exactly, that, with the default network settings.

When I ran the App Engine setup commands again, I got further, but ran into a new error:

ERROR: (gcloud.app.deploy) Error Response: [3] Flex operation projects/projectid/regions/europe-west1/operations/f7d7489b-f4ef-4b8b-ac26-b9b945d3ebfc error [INVALID_ARGUMENT]: An internal error occurred while processing task /app-engine-flex/insert_flex_deployment/flex_create_resources>2022-05-12T09:17:00.642Z6448.wa.0: 'subnetwork_name' must be specified for custom mode network 'default'.

I tried the setup commands with and without a defined subnetwork in the new VPC network I created. The same error persisted regardless.

I have not been able to find any solution to this online so far, so hoping that someone here will be able to assist.

Thanks in advance! Simon

The answer to this was that the default service in the app engine (Services in the left-hand menu in the app engine console) failed to automatically create the VPC- and subnetworks.

By manually recreating the defaultapp engine service, the correct VPC networks and subnetworks were created, and the problem was solved.